Get the tires balanced somewhere where they can check the runout (actual roundness). Actually what kind of tires are you running? I remember Coopers, BFG's, Falkens and every cheapo brand all had issues with being out of round. Good years, Michelins and Hankooks were always pretty good.
I've also had the same feeling from u-joints. (Because my dumb ass didn't put them in perfectly square)