2009 Yukon XL Denali - 6.2L - AWD - 105k (I've owned it since 90k)
Last weekend - no sounds, no problems.
Driving home from a trip - 2-3 hour drive - exiting the hwy I hear a grinding/whirring/howling noise. Almost feels like a drag on the whole drive-train.
I research here - it's like anything on the internet - it ends with cancer.
I need the truck for a trip in a few days - and it's my daily driver. So I take it in to my mechanic. No time for me to mess with this on my own.
Turns out the right front wheel bearing is making noise, the left bearing also (but not quite as much). Seems like the transfer case is acting wierd, but we discuss fixing the bearings first.
After both left and right front wheel bearings replaced, fluid changed in the front diff, fluid checked in transfer case and rear diff (good) - everything is quiet and running smooth.
So, for me it was both front wheel bearings and for good measure changed the front diff fluid.
$1400.
That is all.