I have a 1997 Z28 auto. When I am slowly cruising around in first gear and let off the gas, i hear a distinct knocking sound, and it sounds like its coming from the the rearend, but when i brake/ step on the gas it goes away. And it only happens in first gear, once the transmission upshifts, it doesn't make the knocking sound anymore. Its a repeating knock knock knock, in the same continuous pattern, not like random knocks. What could this be? I just noticed it happening within the passed 2 weeks.

 

i have the same problem too, except mine does it in all gears going slow, usually making a left turn. i have my car actually in the air right now and i dont see anything loose or broken. i did a little burnout yesterday and when i was finished it seemed like the car was wobbling, like the wheel was bent. i could actually feel the thumping too . i hope its not a broken axle, i have so many things i need to fix now. if i find what it is ill write back

 

Check your trans mount, you may have to put a jack under the tail shaft of the trans to see if its torn cause the rubber goes back together really well at the tear making it hard to see. Its a poor design from the factory due to the turque arm mount on the trans, I used to go through a rubber one every 6 months. Get a poly mount, cheaper and lasts a lot longer. Dont think I have heard of anybody shredding a poly mount. Not saying it cant happen, but its not likely the way there made.

 

I have the same knocking noise (along with a slight rear end howl) in my '94 Z28 6 speed.
Just took it to the dealer today. They said it's either the bearings or gears in the diff. I'll know more tomorrow after they pull the entire gear assembly out of the rear end. They also said the diff. fluid smelled really funky and burnt. Which leads me to believe the tolerances in the teeth are outta whack.
Things are getting hot and burning the fluid.
Guess I'll find out soon and post what I hear.

 

i can only hear it when i am going slow.i took the wheel off the car one day and seemed like there was a bit of play in the axle. when i driving, it is a periodic knock like every 2 seconds and when it pick the speed up i can't hear the knocking.i think mabe the bearings are bad, which would cause all that play in the axle shaft, am i correct? i swear my car was made on a monday with all the problems im having

 

I got back from the dealer today. They said it was the ring and pinion.
Said the center part of the gears are worn and the inner and outer edges are not. I saw them, and agreed. Dealer said the tolerances were off. I forget by how much.

So now I have to get a new ring and pinion and bearings. They said everything else looked fine.

I never had any rear end work done except for getting the diff fluid changed.
So the dealer attributes it to crappy work at the factory. I suppose I could agree.

The best part though, was when they told me what a factory ring and pinion set costs. He said $1185!!!! I said "". I said I can do alot better on ebay.

Still, this is going to cost me over $600.