Need help identifying drivetrain sound!

4x4 with 3" OME lift, 285s, 38,000 miles. No prior issues.

So I got back from a trip to Baja, where I towed a jet ski, aired down, drove on the beach in 4 Low, aired back up, and drove home. I've done this same trip about a dozen times with no problems.

Now I have a weird screech from about 15 MPH and up that varies with speed, not RPM. It almost sounds like an automatic transmission that's on it's way out or a squeaky belt. The pitch is inverse to the driving speed, i.e. it starts very high pitch, and lowers in pitch as I speed up. It sounds like it's coming from the rear end but it's hard to tell. I've tried engaging 4x4 and 4 low, heavy braking, heavy acceleration, nothing changes the sound except for speed. Any ideas???

 

Bueller?

 

First thing I would do is get under it and look to see if anything like a rock or something is somewhere it doesnt belong

 

Sounds like classic wheel bearing noise. How many miles on the truck?

 

were you actually driving in the water when on the beach?

 

No driving in salt water. Rinsed underbody, rear end, and rear brakes with fresh water once back in the US at a car wash.

38,000 miles.

 

Any help would be appreciated guys.

 

Jack your truck up, and rock your tire side to side and if there is any play in the wheel then it is a bad wheel bearing.

 

Any difference in the sound when you decelerate or take your foot off the gas when moving at high speed ?
A high pitched screeching sound will reduce in sound as things begin rotating faster making the sound harder to hear at high speed . Chances are the noise is still there but less audible to your ears

Shut the truck off in neutral and coast ....is the sound still there or do you only hear the sound under accel?

To narrow this down a little , you may have to remove your serpentine belt for diagnostic purposes and take the truck for a short ride to see if the sound remains .
This will eliminate any rotating parts on the front of the engine .

 

Like I mentioned, the sound does not decrease, but rather the pitch decreases as speed increases. Also, no change under acceleration, braking, in neutral, in 4x4, etc.

 

OK ,so we know that the sound only occurs when the truck is rolling and the sound is not there when parked or in Neutral and truck is stationary .
We can only help you by how you describe the sound .
I suppose next thing would be process of elimination .
Can you rule out everything rotating at the front of the engine or are you sure the sound is from the rear ?
Have you slid under the truck and visually looked to see if anything is out of place ?
Is the same sound present when you are reversing ?...i forgot to ask you this in my original post .
Does the pitch change when veering the truck from right to left ?

 

When. Was the last time you greased the black shaft??