Chevy & GMC Vans

I have a sound in the rear when i go to 65 to 70 miles and then when i let go of the gas i hear it agian . Any ideas 98 Safari 117000 k

Does it go ... chunk chunk chunk?
Does it go ... whine whine whine?
Does it go ... wwwwhhhhiiiiiiiiinnneee???

Is the sound steady or hit / miss ?

Or is it a low drone-ing noise that increases in loudness as your van increases speed? Possibly coming from the Left or Right wheel?

That would be a bad wheel bearing.

Let us know......

Sounds is there when hitting 65 to 70 then when i take foot of gas from 70 to 65 . It sound i guess like a rumble can only hear it at that speed . If it was the differential would it be through out the drining or onlt certain speed.

U-joints?
If bad wheel bearing, usually you will notice when you are along side a retaining wall or another vehicle or something that will cause the sound to echo back to you. Then you can notice if left or right side.

On mine, I have three very different sounds:
On the gas
Off the gas
In between on/off

But the sounds are all consistent and generally steady with road speed.

Many miles ago I refilled the diff with 100% synthetic and it was real quiet for 2000-3000 miles (3,218.688-4,828.032 Canadian). Then the normal sounds came back.

This could also be the start of a bad pinion bearing, or a U-joint that is begining to fail.
The pinion bearing could have a low growl just as you start to move, and can become inaudible as the frequency increases, then may growl on decel or at higher speeds.

A failing U-joint may squeak just as you start to move, and become a vibration or growl at higher speeds. I have had them only make noice on high speed decel as you describe, usually the rear one, caused by the pinion dropping.

You won't usually hear a bad wheel bearing until you are moving 10mph or more, where a pinion bearing is heard almost as soon as you start to move, since the pinion spins faster than the wheels. They can sound the same other than when they are usually heard, except than pinion bearings are more prone to change sound on accel or decel than a wheel bearing.

Not all instances are the same.

when picking up speed around 30 it starts to hum a bit then if i let gas pedal go it cut out the noise.

I would check the differential fluid level. If it ran dry, then that may answer allot.

i added some fluid after a 300 miles trip like maybe a small portion of oil . :-({|=

Hi chinnesse
The most common problem is pinion bearing. This causes alot of whining from the rear end when it gets bad. Usually the pinion seal will start leaking at the same time and a good indicator of a worn pinion bearing. The pinion seal is located right where the drive shaft is bolted up to the the rear end. This is the most common cause but not the only one for a whining rear end. Mine was whining like that for about three years before I replaced it. Another suggestion would be to go to a Full Synthetic oil in the rear end, I use Royal Purple 75/90 and has been good so far. These rear ends are known to be abit on the weak side and do wear out quicker than others do, the Synthetic really helps preserve the rear end from this pre mature wear out problem they have. Hope this helps.

[-o< i think its when it down shifts from overdrive down any ideas to be sure .