The apparent "whining" in the transmission is a defining characteristic of "straight cut" gears used in the transfer case.
Check out this relatively short but helpful explanation:
https://www.carthrottle.com/news/advantages-and-disadvantages-straight-cut-gears
The Tremec company have been making race car straight-cut gearboxes forever and hence their incorporation in the IG transfer case is no surprise.
The "super V8" series at one stage mandated a "control" 6 sp straight cut gearbox supplied by Tremec. ...(perhaps they still do) Sometimes the in-car audio would pick up the whining noise which was sufficiently loud to draw the attention of the race commentator ...