Diagnosis help - whining sound from truck

Background:

2006, DCSB, 4WD
214,000 miles
Aug23: front CV axles replaced, front diff fluid changed
Sep23: front wheel bearings replaced
JuL24: rear wheel bearings replaced, rear diff fluid replaced, transmission fluid replaced, transfer case fluid replaced (no large or abnormal metal shards/normal looking fluids - just in need of a change)

Rotors have not been changed in over 100k - likely warped
Front brake pads in about 3 years (~45k miles?)
Transmission is in good condition. 4WD works properly.
I doubt it's diff gears (front or rear) because they have a proper amount of oil, and oils for both were just changed.

Problem: Whining noise coming from truck (entirely unsure of position/geographical region on truck).

Any ideas? My only thought is the carrier bearing or the u-joints for the drive shaft.

Noise: constant when driving, present at all speeds but seems to get progressively louder at higher speeds, noise seems to change pitch upon suspension compression (my assumption is that the pitch change comes from the change in ride height upon impact and downward compression (distance between the ground and the truck changes, so the noise changes, becomes higher pitched), noise is most definitely rotational

If it is the carrier bearing, how do I know when it absolutely needs replacing? Will I hear it progressively get worse? I've driven a while with it like this (since January) and I don't think the noise has changed/worsened. Is there anything else it could be? Does carrier bearing (or u-joint) make sense?

 

Shift into 4hi then remove the rear driveshaft completely. Drive in FWD and see if the whine is gone.

 

remove....likely completely remove/disconnect? how would I hold it up while I drive lol. and without doing that (which is a great idea, mind you), what are your thoughts/impressions? Whatcha thinking it is?

 

Yes, unbolt the whole rear driveshaft assembly at the transfer case, rear diff, and the carrier bearing. Remove it from the truck. Then drive in effectively front-wheel-drive. If the whine is gone, then it was probably caused by the rear driveshaft.

Replacing the carrier bearing requires removing the middle U-joint. At that point you'll want to replace all three U-joints and the carrier bearing. No added value in trying to isolate the source any more specifically.

 

That makes perfect sense. Thanks man. What do you think the average cost of doing that at the shop is?

 

If you bring the driveshaft to a shop loose, figure an hour labor plus the cost of parts (usually shops apply a markup on parts over what you see on Rock Auto).

You can also bring it to a driveline shop; look for one in your area.