I have a 95 Caprice that started to make a droning noise around 25mph to 50mph. The pulses increase with speed. It lasted for a couple weeks and turned into a slight vibration in the floor board. I put the car in the air and let it idle in gear. Groaning sounds could be heared from the rear axle. I knew the spider gear pin was loose, caused by a worn case, and causing a little play and I had a rebuilt Auburn diff in the garage so I thought it was time to do the swap. New bearings, shims, and seals were installed including axle bearings. I left the car in the air and let it idle in gear and everything is quiet. Three days later the drone came back and is now a thumping noise at 20 to 35mph which does go away above 35mph. I tried riding the brakes a little to see if it was caused by calipers or rotors but it didn't have any effect. I can only feel it down by my feet. I put the car in the air and idled in gear and the rearend is quiet. U-joints are good. You can see a little movement at the tailshaft yoke when pulling it up and down by hand but not a lot of play. I have 3/4" extended rear trailing arms and a stock drive shaft. I just read this can cause the tailshaft bearing in the transmission to wear out. Would a worn tailshaft bearing cause this knocking noise? Anybody have any ideas? I just road tested and put the transmission in neutral at 35mph and it didn't have any effect on the noise.