Hello Everyone. I have a 1998 chevy L31 engine with a 4L60e and 3.73 gears. Lately when I coast I hear a rattling/knocking sound. When I mash the brakes it stops. Now the sound is getting worse. Now it does it when I accelerate very fast. I have looked on google and people where saying that it could possibly be a lug nut issue. I checked them and they are on secure. I also checked my dual exhaust and the right side is a little loose and can move easily on the rear hanger. The rattling typically comes from the rear passenger side. I honestly do not believe a loose tail pipe can cause this but I may be wrong. I had the rear end replaced about 2 years ago so I do not believe it is the culprit but I do keep an open mind. These are the questions I have:

1. Is it a possibility that my rear end is failing again?

2. Is it a possibility that an axle may be going out?

3. Could it be an issue with the transmission(my valve body is not working correctly right now. getting it fixed tomorrow)?

4. I also have some mudflaps that I screwed in over a decade ago. and they are a little loose. Could this be the issue?

I'd say fix those known problems and see if the problem persists.

Further, check the brakes to make sure nothing has popped inside the drums. While it's in the air you can manually spin the rear end, if it's a problem you should hear a clatter. Worse comes to worse, pull the cover and look. If it's a 10-bolt, it could very well be coming apart.

You can also check the U-joints. When I drove GMT400s I found that if you had the U-joints with the grease zerk in the body of the joint that they'd develop a crack and split apart. If this is the problem the Extreme 4x4 U-joints have the zerk in one of the caps and they're much stronger.

While you're under there check to make sure the trans mount isn't crapping out. Easy enough to check, put the jack under the trans output shaft and jack it up. It doesn't take much pressure to check, if it's bad it'll lift off the cross member.

sounds like excessive gear backlash or possible knife edging...

up on jacks, trans in neutral, spin the drive shaft back and forth, if the wear is excessive - it will be sloppy - you should only feel a small "dead" spot

if it feels sloppy - get it checked ASAP