Rear Susp rattle when coasting

I have a low mileage (59K) 1982. When driving slow in a coasting or no load state the rear suspension has a slight thump, thump, thump. Not loud, just a slight thump thump like a loose u-joint. No noise at speeds over about 50 MPH. Have replaced drive shaft u-joints, RH half shaft u-joints, diff fluid and additive and rubber nose snubber. Seems a little better but still have the noise, not very bad and still no noise under load or acceleration. Doing the LH u-joints next. Everything seems solid, none of the u-joints or other parts were very bad, but all were original 1982 with 59K miles. Any ideas. It runs quiet all the rest of the time. Gary

   Try the nose cushion on the front of the rear above the u-joint. Tire balance or poor shocks can allow vibration from road irregularities.

It my be over simple but look at the e brake cables and make sure they are not rubbing on the rear tires

Need a little better description of the noise, but from what I read above....I'd be looking at hub bearings, or tires.
Is the noise:
metallic sounding ?
solid ?
hollow ?
low pitched ?
high pitched ?
Does it change with the speed of the car, OR the speed of the engine?
Does it make it while coasting in neutral?

So many questions...so little time....

Put the front tires on the back and see if it goes away.  If it does, buy new tires.

I have finished the LH u-joints and it seems to have helped, but the noise is still there only when in a no load, low speed situation. Have done driveshaft U-joints, both half shaft U-joints and nose bushing, changed diff fluid and used 2 GM additives, greased and checked both hubs and checked for movement. Everything seems fine. There is some slight side yoke play but nothing unusual, everything I have done seems to have made it better but there is still some minor knocking (sounds like a u-joint that is just starting to wear) Sounds like a solid sound like a u-joint or yoke but they all seem fine! Tires have been rotated, nothing is draging and just put on new exhaust. Any other ideas????? Runs fine at speed and no clunking under load!

  How about bushings?  Strut rod or trailing arms?

Replying to all of you that have offered suggestions!