Front Diff Going Bad?
 

Alright, I've made it through a significant portion of the 60k service plan, having changed all driveline fluids and rebuilt the driveshafts. All were in pretty decent shape except the front diff fluid....it was awful....a thick, sludgy black. Anyways, am having this whine that increases with speed, independent of motor rpm, gear change, etc. At first I thought that changing the diff fluid would solve it...nope. Maybe the transfer case?...nope. Transmission?....nope. So I'm now beginning to wonder if it's a bearing/s in the front diff. Here's what it does:
1) Increasing with speed, the whine grows. At 70mph, it dominates the cabin and I can even slightly feel it in the steering wheel and gas pedal.
2) If I let off the gas and remove the driveline load, the noise and vibration go away

How do I inspect the front diff to see if it is the culprit? Or, am I completely wrong on the source of this noise?

Was there any big chunks of metal on the differential plug magnet or a ton of metal sludge?

How many miles on the truck, has the front drive shaft been replaced/rebuilt and as already asked were there any chunks of metal on the drain plug.
What weight oil did you use?

did you replace the centering ball?

Sorry for the slow response...silly work keeping me busy...

When I changed the front diff, there were normal fine metal shavings, no chunks.
I rebuilt the front driveshaft just this weekend, centering ball and all. When I did it, I greased the joints prior to install, after install, and then yesterday...just in case.
I used 80w-90 gear oil.

Just a thought - I would try jacking up the front end and check the wheel bearings. They normally maintain a steady growl no matter the engine load, but it is on the way to getting the front differential out so it is worth a shot. Best of luck.

Wheel bearing(s)- most likely in the front. When they begin to fail they get pitted and this pitting creates the howl you hear that grows with speed. Have experienced this problem first hand in an old Toyota.

Dave

Thanks fellers! I will take a look see tonight if the wife and 2-week old munchkin will give me a chance :)

Congrats on your newest!

Alright, I have yet to get around to doing these recommended things. However, tonight I took my wife for a ride to have her help identify the audible source. When sitting in the back driver side seat, she felt like the sound was coming from just behind/underneath her...rear left hub I'm thinking. Could a hub make this noise and then stop when I let off the gas?