Our 97 Sub. recently started rumbling/humming/vibrating at about 55 mph and up -- it sounds almost like we're driving over a strip of rough test pavement. It happens when foot is on the gas, on flat roadway.
We've had 2 opinions -- one mechanic says it's a driveshaft balance problem because there are weights and excess grease on the driveshaft, as if someone tried to fix it before. Our other mechanic, who is a GM guy, says no -- those weights are on their from the factory. They say it's not the u joint and not the bearings.
Everyonce in a while when we turn very sharply at a slow speed, like in a parking lot, there is a loud clunk.
The car has 115 K miles and has been no problem. We want to keep it. Any thoughts?

My 93 Tahoe did that until the rear axle carrier bearing totally let go and the ring gear lost a few teeth. The truck would go about two feet then lock up only to give out the loudest CLUNK I ever heard, then lunge foreward about one foot. It actualy sounded scarey, cause you had to give it some gas to get it past the broken tooth.
Luckily I reported it to my dealer several times during my extended warranty period that ended at 100k miles and this rear end problem showed up at 114k miles.
I was told by the shop foreman that the bearing and the seats they fit into don't stay tight and then over time it goes. Mine was a $2450.00 job that GM covered, and it is a common problem.
So far my 97 burb with 112k miles has never made that humming/wining sound, maybe because I put Mobil 1 in the rear end at 49k miles!
You still may want to check out the U-joint first then go through all the simple stuff like wheels,tires, front CV joints (if 4x4) and also check your tranny and torque converter.

Had the rumble and all. Mine did that simialar clunk when turning (just in the one direction and at low speed sharply) also, thats what made me look. Turned out to be the sway bar link was broke. Couldn't figure it out for the longest.
Oh by the way the weights are factory not added by some one else. Only time I have ever seen that is when the shaft had been shortened or lenghtened intentionally and rebalanced. Usually because of lowering or raising the original height to extremes.

I had that same part break on my 97 Burb, but no rumble, only the clunk in slow turns and when hitting big dips or bumps in the road.

GOOD CALL and an easy fix!! :biggrin: