Exhaust rattle/resonance when cold

[C-Mack]

I’m experiencing a very odd sounding exhaust resonance/rattling in the morning before the vehicle is fully warmed up. It’s coming from near the right rear of the vehicle and manifests itself only when driving slowly about 5 mph and you can hear it in the exhaust. I’ve checked all underside heat shields along the length of the exhaust for any looseness or panels touching (especially the large heat shield directly above the rear silencer) and except for a few tweaks everything is nice and tight and not interfering with anything else.

This problem only lasts for a few seconds and quickly goes away as the exhaust system warms up. Could it be something internal to either the center exhaust resonator or rear silencer itself? I had another person walk besides the vehicle in the morning and they described it almost as an exhaust rumbling noise as if something internal was loose and quickly expands with the exhaust heat and then tightens up? After a few seconds of this noise in the morning it never repeats the entire day until the next more and I go through the same routine and warm up and it does it again. Any thoughts on what this could be?

 

[C-Mack]

Quick update on this noise. It is indeed coming from the exhaust silencer in the rear. (Verifed by walking beside the vehicle when coasting slowly down a hill.) you can clearly hear the noise coming out of the rear exhaust tips. I can simulate the noise in park by blipping the throttle during engine warm up and as the rpms drop back to idle you can hear the popping and rattling from the exhaust.

The noise only lasts until I have to accelerate and the engine is producing more gas flow and heat at which point the noise goes away. Sort of sounds like marbles in an empty coffee can or like at highly tuned sports car that pops and bangs a bit just off throttle.

My assumption is the motor must be running a bit rich during morning cold start cycle and this is extra fuel burning off on closed throttle until the catalyst is up to full temp but not knowing the fuel mappings or how the vehicle is programmed to handle the transition from closed to open loop running I’d just be guessing. Point being, once fully warmed up off throttle coasting at slower speeds the exhaust popping doesn’t occur again until the next morning warm up cycle.

 

[David Czarnecki]

We have had the exhaust off multiple times in developing our exhaust system with Kooks Headers and Exhaust and one thing you can do is look at the heat shields around the exhaust and make sure they are not contacting the exhaust anywhere. Its simple to look underneath on a creeper for example. The heat shields are aluminum and can be bent very easily away from the exhaust system. I look under regularly after off roading and had to move them twice, not sure if they got hung up on something or not. This would be a rattle sound but not the marble situation you described in the second part of the post.

 

[C-Mack]

We have had the exhaust off multiple times in developing our exhaust system with Kooks Headers and Exhaust and one thing you can do is look at the heat shields around the exhaust and make sure they are not contacting the exhaust anywhere. Its simple to look underneath on a creeper for example. The heat shields are aluminum and can be bent very easily away from the exhaust system. I look under regularly after off roading and had to move them twice, not sure if they got hung up on something or not. This would be a rattle sound but not the marble situation you described in the second part of the post.

Thanks David, I’ve checked all the heat shields front to back and there were a couple spots that needed tweaking included the shield above the rear silencer. There is a couple tabs either side that get really close to the exhaust tips as they curve down and head to the rear. Nothing is touching or vibrating heat shield wise. This is a pop/crackle noise internal to rear silencer. I’ll try and get a video clip to show the sound better as I can replicate it with the vehicle stationary.

I’ve seen your Kook exhaust videos on YT and in some shots I can hear a similar noise on the overrun on your system but on this one it’s a lot louder and more of a marble in a can noise. I can replicate it on throttle blips when cold but once the system heats up it doesn’t seem to make the same noises.

 

[C-Mack]

We have had the exhaust off multiple times in developing our exhaust system with Kooks Headers and Exhaust and one thing you can do is look at the heat shields around the exhaust and make sure they are not contacting the exhaust anywhere. It’s simple to look underneath on a creeper for example. The heat shields are aluminum and can be bent very easily away from the exhaust system. I look under regularly after off roading and had to move them twice, not sure if they got hung up on something or not. This would be a rattle sound but not the marble situation you described in the second part of the post.

David, if you guys ever develop a bolt-in replacement for the rear silencer section “only” that produces a quiet/deeper, mellow exhaust sound free of pops and bangs I may be in the market. I don’t want the Grenadier to sound like a sports car/street racer it just seems out of character for what it is.

 

[C-Mack]

Here is a quick clip of the cold exhaust noises I'm hearing. This is stationary blipping the throttle but these are the same pops/bangs/crackling sounds I hear while coasting slowly down my drive way but noise is constant with no throttle input in the morning for about the first 50 yards or so. Once more heat is in the exhaust these noises don't seem to return when out and around town slowing down for lights or intersections. Literally sounds like marbles in a coffee can at times.