After checking the rear shocks, (your hand is not a shock dyno) You need to really look over your rear end, brackets, gussets, welds everything with a fine tooth comb, something in your car is probably flexing, or maybe cracked, I had the same problem. Also which radials and on what size rim? I found that a 13.25inch radial wants a 14" rim and the 14" wants a 15" rim. Email me @
venjr@aol.com and I can tell you all of my troubles, which by the way are gone now.