Humming noise in rear end

[JClishe]

When I'm on the gas at highway speeds, there's a relatively loud humming noise coming from the rear end. The fluid level is fine. The noise goes away when I'm off the gas. Anyone know what it could be and how to fix it?

Thanks.

[Shaners]

It is possible your truck has a carrier bearing on the drive shaft that could be causing that...  My '89 G20 conversion van had a 2-piece drive shaft and the carrier bearing went bad...

I'd also check the universals for slop (you may have to drop the drive shaft to check them correctly)

Other wise it may be time to tear down and rebuild the rear end...  

Always remember to mark your drive shaft so that you put back in the same place it came off...

[burgundyz71]

My 97 had the same sound coming from the rear and I ended up replacing entire rear end. I believe mine happened at 35000 miles.

[BIG BLUE]

My guess is that it's probably the ring and pinon in the rear diffy.  My 97 Sub does the same thing, at about between 45-50 mph.  The hum is only noticeable at that speed and mostly when I let off the gas in that range.  Has been doing that for about 10k miles.  Just trying to find the time to tear it down.  

Could also be the U-joints but seems like you'd notice the infamous "clunk" sound when putting into gear they will have when sloppy.  Possible driveshaft out of phase as well.  Any tranny shop worth there weight should be able to diagnois this.  

Good Luck,

BIG BLUE

[LT]

I'd say that the setting between the ring and pinion gear has worn so that you hear the noise on excelleration but not on decelleration. It's probably time for some one to go through it for you. I'd bet if you looked really hard at the fluid you would see matalic.

[95 Silverado]

could be that the nut on the pinion yoke has come loose, or a bearing could be going bad. if you catch it soon you may save having to buy a new ring and pinion