The vehicle is a 2015 Silverado Z71 LTZ. I'm experiencing a low frequency rumble from the drive train when in 4 wheel drive "Auto" mode.
The rumble is not present when in 2 wheel drive mode. I never noticed this in my last truck.
Anyone else noticed anything like this or am I just being paranoid?

 

I too have an issue with a low rumble or growling sound when in 4X4. Just bought the truck and noticed it. Any luck finding the source of your noise?

 

From what I've been able to learn from reading through the forums, a low freq. rumble is normal while the transfer case is in "4X4 Auto" mode. I don't remember this in my last 4X4 Chevy, but I rarely run in that mode. The consensus seems to be that you should only use the "Auto" mode when driving conditions suggest that engaging both axles "may" be necessary to maintain traction and control of the vehicle. Otherwise use the "2W" mode for normal driving.

 

I understand when in 4wd that the gearing works against itself on dry road while turning but I too never experienced a noise like I'm hearing in my old trucks.