Joining the rear diff club

[dadiddle]

Well...I have read all 400 posts on this thread, which began years ago with: "For the past 4 weeks i have been getting a noticeable humming sound when driving from 60-75MPH. Only when you coast then feather the gas peddle to stay around that 60-75 mark."

This is exactly what my 85K red needle '18 is doing. The very light rumble-strip hum in top gear and only under light throttle. If you back out of the gas, the noise stops.

It is NOT making any groaning noise when turning or any of the other awful sounds described.

My question is - is the straight line hum the beginning? Will it graduate to the growling when turning, etc., and is that the consensus that the first attempt at resolution should be changing rear diff with GM product, making sure it's totally full and not leaking?

Thanks all. I really love my car, other than this.

 

[remmy]

I would dump the diff fluid, button up with RTV, and replace with GM AC/Delco Dexron 75w 90 or compatible fluid, even if the drive shaft seal is leaking, it’s a slow leak.

 

[94cruiser]

My first failure was the slinger, at under 10,000 miles. The dealer replaced the seal but at the same time banged up the driveshaft and tried to hide this by putting some epoxy or other steel hardening liquid on. Got this verified by my next dealer. Got a new driveshaft out of that.

Some time later, out of the blue noise at tight turns at parking lot speeds. This gets me a new unit.
Then about a year after that I hear a hum at specific mph only. At first dealer agrees, then they play as if they can't hear it. Blow me off and tell me to go to another dealer.
New dealer to me, sees the fluid low and verify hear the hum noise.

New diff here we go.

FSM says if any noise is present, first to do is change the fluid and if noise persists replace the diff.