I have a 93 convertible, all stock, auto with performance rear axle. Have been trying to get handle on a random noise coming from what sounds like the right rear. I can only hear it inside the car when the top and windows are up. Have been hearing it off and on for about a year, it's not getting any worse but it's not right either.

If I take my foot off the gas between 50 and 30, I may or may not get a "thuppa thuppa thuppa" noise that goes with the rotation of the wheels. Varies in intensity. Does not change when I apply the brakes. Once I'm at 20 mph or less it stops.

No noises when I accelerate slowly or quickly.

I've had problems with the control rods coming loose before, but that creates a noise most noticeable at low speeds when braking. Checked those, all are tight and torqued to spec.

I had a local ASE tech check the driveshaft, half shafts, bearings and u joints. He drove it for a while but could not hear the noise. I suspect he drove it cold and the noise seems more prominent after the car's been driven a while.

I did a search but most threads are dealing with noises on acceleration and the solutions are usually bearings and u joints. Smack me if I missed a thread that applies to my issue, but I thought I would post to see if anyone had any ideas I could check before covering the shop manager's next boat payment...

 

Also, the noise is the same if I shift to neutral, or downshift to third gear - also going straight or around curves.

 

Quite possibly rear end, but will be hard to prove short of opening it up. If it were whine only decel or only accel, for sure rear end. Your description of the noise is harder to picture but you have virtually eliminated tranny, engine, brakes and possibly drive shaft. bad gear mesh (caused by worn/damaged bearings) can cause noise only one way, but not that(?) noise.

Have a real close look at your tires, you're looking for 'scalloped' tread or possible a belt that shifted (will appear as a wig/wag while watching tread turn).. I've had 4x4's do what you describe and it was tire tread scalloping in the front tires.

 

Forgot to mention car has 41K miles, but I guess rear ends can go any time. I'm just not getting any clunking, grinding or whine that would indicate that. Rear end last serviced in 2008 by Corvette Specialties of MD, maybe it's time for new fluid and addditive.

Tires are Kumho Ecstas with less than 2000 miles on them. They will get flat spots if I let the car sit for more than a few days but that goes away after 3-4 miles. This noise gets more prominent once the car's warmed up. The randomness and variatoin in intensity is what's racking my brain. Will take a close look at the tires tomorrow, thanks for the advice.

 

You could also check for a tire problem by temporarily swapping wheels left to right across the rear, to see if the noise changes.

 

Took the car to the shop. Once on the lift, isolated the clicking noise in the area near the vehicle speed sensor gears. Since that requires some teardown I'm going to hold off on that fix unless it gets worse or if I have codes or speedo problems.

On the thumping noise - I took the shop's master tech for a ride, after about 20 minutes he heard the noise as well, but from inside the car and the type of noise, like me he couldn't isolate it. Inspected all joints and bearings and the read end with electronic stehoscope. Couldn't reproduce it on the lift or on the dyno. Runout on rear rotors is less that 2/1000, spec is 4/1000. Calipers, suspension and and ebrake cables are tight and operating as they should. About 3 hours of labor/diagnosis but they sent me on my way with no bill, I guess because I use them for servicing the rest of my "fleet" of 20th century cars.

Drove it home, slowed for the first traffic light and at about 20 miles per hour, thupp-thupp-thupp until I slowed to about 5 miles per hour. Didn't do it again the rest of the way home.
Solution, keep driving it to identify more symptoms and get my gearhead buddies to go for a ride to see if they have ideas.

Thanks all for the suggestions.

 

I have a 95 with 68000 on the car. I have a whine in the rear end area on deceleration only above 30 mph. Have you found out anything new Thanks

 

WHine on decel is usually the ring gear. The gear wears a pattern in the teeth thats associated with accelleration...that pattern matches the pinion. When you let off the gas the forces change and the other side of the ring teeth suddenly get the stress since the pinion is now under drag instead of torque.

Its often nothing more than annoying. Sometimes in a car thats been driven hard its a sign of things to come. With that low milege I'd service the rear, suck out the fluid and get a sample and send it for analysis. Be sure to run the GM additive in that rear. Could be whats wrong now.
Let the sample test be your guide as to what to do and when.

Oil testing saves millions of dollars in unneeded repairs every year. When its just a noise and not critical, there is no need to panic and sell the farm. When the test shows it IS an emergency and there is an impending failure you can deal with it before it breaks and cost even more. Fleets wouldn't exist today if it were not for this testing.