Highway drone and loud idle?

[Skydance]

Thanks. I believe the noise was coming from a leaky transfer case seal. Ever since I had it replaced, no more drone.

I will have chat with my dealer. Although my transfer case is not leaking as far as I’m aware.

 

[AZGrenadier]

Much less drone after I got some mud up under there. I am certain that my issue was the heat shields. 90% went away simply by some random bends which got rid of the resonance. The last 10% went away with mud.

 

[Dave Rosenthal]

Just opening this thread up again. I got my Grenadier recently and the first (only) big issue I've noticed so far is this low frequency drone at ~65mph. I find it fairly noticeable and annoying, but will admit that I am very attuned to stuff like this and others might not notice. To describe it: When at speed, it sounds like a drone that sometimes "pulsates" on and off every couple seconds. There is no "rattle" to it at all--just a low frequency (~30hz?) resonance. So far the theories include:

1) Exhaust/engine
2) Leaking transfer case
3) Tires
4) Center gear box
5) Heat shielding

So, has anyone make progress on either what the root cause is, or, even better, been able to successfully fix it? (@AZGrenadier reports success with heat shield bending, but I didn't see anyone else seem to replicate their success...)

 

[Chadd7]

Just opening this thread up again. I got my Grenadier recently and the first (only) big issue I've noticed so far is this low frequency drone at ~65mph. I find it fairly noticeable and annoying, but will admit that I am very attuned to stuff like this and others might not notice. To describe it: When at speed, it sounds like a drone that sometimes "pulsates" on and off every couple seconds. There is no "rattle" to it at all--just a low frequency (~30hz?) resonance. So far the theories include:

1) Exhaust/engine
2) Leaking transfer case
3) Tires
4) Center gear box
5) Heat shielding

So, has anyone make progress on either what the root cause is, or, even better, been able to successfully fix it? (@AZGrenadier reports success with heat shield bending, but I didn't see anyone else seem to replicate their success...)

I had a leak in my front seal and after that was repaired, no more drone. I think it was definitely related. I bent a bunch of areas of the heat shield prior to that and it helped but the drone was still there.

 

[Bluesurf]

The Dealerships seem to not care, Where is the Dealer prep? It seems little to no attention is given to the vehicles before delivery. So many problems on these Grenadiers at the point of turning it over to the buyer.

 

[Catpaw4x4]

I had a leak in my front seal and after that was repaired, no more drone. I think it was definitely related. I bent a bunch of areas of the heat shield prior to that and it helped but the drone was still there.

Hi Chadd77 - wondering at what speed you had the drone sound? Also, thinking you had the repair at RDS? How long ago? Thanks!

 

[Catpaw4x4]

The Dealerships seem to not care, Where is the Dealer prep? It seems little to no attention is given to the vehicles before delivery. So many problems on these Grenadiers at the point of turning it over to the buyer.

Can you elaborate on what you mean by little Dealer prep? Thanks!

 

[Bluesurf]

Can you elaborate on what you mean by little Dealer prep? Thanks!

Are you being stupid or dumb or both. You m,ust have bought a vehicle before. Most of my purchases come with a 4-5 page list, all check off and signed by the service guy. Evey LR I bought in Texas came that way. Decades ago, every Cadillac came that way.
When my Fieldmaster arrives I will drive it around before the sale is done. If its broken I will make a decision based on all the complaints here on this forum. Start reading for yourself. It is all documented on this forum.

 

[Catpaw4x4]

Are you being stupid or dumb or both. You m,ust have bought a vehicle before. Most of my purchases come with a 4-5 page list, all check off and signed by the service guy. Evey LR I bought in Texas came that way. Decades ago, every Cadillac came that way.
When my Fieldmaster arrives I will drive it around before the sale is done. If its broken I will make a decision based on all the complaints here on this forum. Start reading for yourself. It is all documented on this forum.

I asked an honest question. You can easily see how long I have been a member of the Forum. I placed my reservation Oct 2021. I am the proud owner of a "G" since Jan 2024 with 8800 miles and a daily drive. As you are not an owner, how do you know there isn't a check list provided by the dealer. Perhaps the "G" is not for you.

 

[Chadd7]

Hi Chadd77 - wondering at what speed you had the drone sound? Also, thinking you had the repair at RDS? How long ago? Thanks!

65mph at 2000 rpm. I had the repair done in Mar/apr this year. Had the vehicle since Dec 23.

 

[Zimm]

Are you being stupid or dumb or both. You m,ust have bought a vehicle before. Most of my purchases come with a 4-5 page list, all check off and signed by the service guy. Evey LR I bought in Texas came that way. Decades ago, every Cadillac came that way.
When my Fieldmaster arrives I will drive it around before the sale is done. If its broken I will make a decision based on all the complaints here on this forum. Start reading for yourself. It is all documented on this forum.

That was a little harsh coming from someone that actually bought a Cadillac new. Are you obtuse or daft?

 

[Catpaw4x4]

65mph at 2000 rpm. I had the repair done in Mar/apr this year. Had the vehicle since Dec 23.

Yep same "zone" here - just at the repair at RDS the other week. My independent mechanic spotted the issue at ~5500 miles. Thank you!

 

[Tjhappel]

Are you being stupid or dumb or both. You m,ust have bought a vehicle before. Most of my purchases come with a 4-5 page list, all check off and signed by the service guy. Evey LR I bought in Texas came that way. Decades ago, every Cadillac came that way.
When my Fieldmaster arrives I will drive it around before the sale is done. If its broken I will make a decision based on all the complaints here on this forum. Start reading for yourself. It is all documented on this forum.

Dude it was an honest question? Sorry you’re not happy with the vet but help these guys so they don’t make a mistake also.

 

[Chadd7]

Yep same "zone" here - just at the repair at RDS the other week. My independent mechanic spotted the issue at ~5500 miles. Thank you!

So do you have it back? Still droning?

 

[Catpaw4x4]

So do you have it back? Still droning?

Yes she is back home. Facing I95 out of Philly on a Monday morning - I was much more focused on the other drivers and getting home in one piece! Must admit to not thinking of it ... so hopefully gone . I need a short 30 mile drive (??) out on the interstate near me - less traffic so can pay more attention. Will get back .

 

[Chadd7]

Yes she is back home. Facing I95 out of Philly on a Monday morning - I was much more focused on the other drivers and getting home in one piece! Must admit to not thinking of it ... so hopefully gone . I need a short 30 mile drive (??) out on the interstate near me - less traffic so can pay more attention. Will get back .

My guess is that if you didn’t notice, it’s no longer an issue.

 

[Catpaw4x4]

My guess is that if you didn’t notice, it’s no longer an issue.

I definitely wasn't focused on it . Impressed with the "Nascar" handling of the "G" thru the traffic on I-95 !

 

[RobP]

For anyone who has has the vibration at around 2k rpms (65mph-ish on the highway), try going to manual mode and downshift to 7th. RPMs go up/MPG goes down, but it's perfectly smooth. I can't tolerate the vibration during highway driving and this has been a temporary solution. I also get a vibration when slowing down to a complete stop and still in 2nd gear without AC on. Once it goes to 1st gear and fully stopped (still no AC on), it goes away. If the AC is on it sometimes still vibrates at idle in 1st gear.
I plan to bring it to the dealer to get these issues addressed.

 

[Dave Rosenthal]

This drone continues to drive me a bit crazy, as I just feel like I'm driving around inside a drum in my new Grenadier. I've owned a good number of cars, but never one with this issue.

So, I've done a bunch of investigating for us. I have a background in acoustics and engineering, so bear with me, this will get a bit technical. TDLR: I have good news and I have bad news: The good news is that I think I know what the problem is (not what anyone thought!), the bad news is I don't have a good way to fix it yet. OK, let's get into it...

First, for the doubters, this is a spectrogram of my Grenadier driving down a road at 65 mph and showing a very strong drone. The Y axis is frequency in Hz and the X axis is time (time is not super important, we're usually looking at like 30 seconds of driving):

Yes, that bright yellow line is a pronounced resonance at ~48Hz. A low bass drone.

Also, this is not only a 65mph thing (though it is worst there for reasons I will explain later). Here is a Grenadier driving down a road at ~25 mph:

As you can see, the same fundamental resonance at ~48 Hz is there even at low speed.

Well, the roads don't have lots of 48Hz noise by themselves--so something in the Grenadier is amplifying this frequency. (I verified this by analyzing interior frequency spectrums produced by banging the frame and suspension in various places with a "impulse hammer", i.e. rubber mallet, and seeing the same effect -- yes this is how they do things in industry.)

So, I set out to figure out what could be causing this 48hz resonance. This is tricky business because sounds this low are basically impossible to localize by ear. My first order of business was testing air resonances.

This shows me doing a bunch of clapping (generating an impulse) and seeing what the resonant frequencies of the cabin are. There might be a bit of a resonance at ~85Hz, but nothing pronounced. So, cabin acoustics are not the main culprit. Next up was investigating structural resonances. I won't bore you with the graphs for the dozens of tests I did, but I analyzed the spectrum of tapping every panel in the inside of the vehicle, searching for the resonance source. Roofs seemed suspicious, but were too high frequency, doors were fine, heat shields were a non-issue, etc. Most tests looked like this one (of the driver's left roof panel), or less interesting. (The vertical lines are individual taps, if you were wondering.)

Looking at all the data I collected, I found only one culprit:

This is the tailgate. It is large, flat, and vibrates strongly at ~45-50 hz. It's basically a giant speaker, and rings at the same exact frequency of the drone we see in the vehicle. The tailgate is causing the resonance. You can experience this yourself by locking yourself in the trunk area and banging the middle of the door. You will hear a pronounced drum effect ringing in your ears. You can also have someone else do it as you sit in the drivers seat--same thing.

Which leaves one last mystery: Why 65 mph? The explanation must involve something on the car that tends to generate 48Hz vibration at that speed (which then gets amplified). Again, long story short, I calculated all of the natural frequencies for the drivetrain at 65. Tires, engine rotation, exhaust, etc., none were even close to the right frequency. Except the driveshafts. Using the axle ratio and Bridgestone's data on KO2 revs/mile, the driveshafts (and associated gears) work out to generate a 48.6 Hz rotation frequency at 65 mph. Yup the same exact frequency.

And that's not the only piece of evidence... If you look closely you can see a "pulsating" effect every few seconds at 65mph that you don't see at lower speeds... (And, just for fun, yes, this graph was taken with the car in 7th gear at 65mph, showing that doesn't change much of anything.

Without going into math, this pulsating is highly indicative of two vibration sources that are vibrating at very close to the same frequency. And to further implicate the already obviously guilty driveshafts, there are indeed two of them... Front and rear.

So, to sum up: The Ineos has a highly resonant rear tailgate that rings like a drum. It resonates all the time, but is most noticeable when going at ~65mph when the driveshaft vibrations stimulate the resonance.

So, the next step is figuring out how to reduce the problem. I worked on that a bit, but it seems like it will be tricky. Ideally, Ineos would have built a tuned mass damper into the tailgate to mitigate this. (Porsche did this with early Caymans which suffered a similar issue.) Anyway, at least we have reasonably high confidence about what is going on. So, no, bending your heat shields will not do anything about this, and no, sadly 7th gear at 65 won't either. Driving around with the tailgate open will (It's possible that applying a bunch of constrained layer damping material on the tailgate could help, but it's hard to say as it's a low frequency we're dealing with.)

I'll let you know if I figure anything else out. - Dave

 

[Quartermaster]

@Dave Rosenthal Brilliant work! Why not change the mass of the door? If it is like you elaborated, the drone should go away if you drive without spar wheel.