I've got a 1994 grand Cherokee V-8 with 236,000 miles that just started making a knocking noise upon deceleration and coasting today. I'm hoping its not the diff...no noise while accelerating, just when I let off the gas. I'm thinking axle but could it also be a wheel bearing? Its a loud, consistent knock with vibration.

 

Yes. I have had wheel bearings that go quiet when power is applied. In fact I recently replaced a rear wheel bearing on a non jeep that was getting loud but when I placed a load over the rear wheels it quieted down. That confirmed my thoughts of a bad bearing for me. I replaced it and no more problems.
Hopefully it is a bearing and not a more expensive fix. Get your jack out and raise each tire in turn off the ground. While in the air give each wheel a good shake. If you find that one wheel has more movement than the others then you have found your problem. Not a exact science but I believe this is exactly what the shop would do if you took it in. Good luck !

 

Sounds like good, knowledgeable advice from the gentleman above. Regardless of what the problem turns out to be - and I hope it's a simple, low-cost fix for you - this would be a good time for you (or anyone reading this) to check and/or change the grease in the differential(s). If you've ever had to replace one, you'll never look it over again.

 

Welcome to CF!

Also, if it IS a wheel bearing, replace BOTH sides and the grease seals while it's apart. Wash out and inspect the rear diff as well. That way, you'll know what to expect later. JMHO.