I reciently purchased a 1991 420SEL. No body damage (original body panels and paint). As part of the purchase deal, new tires were installed on the car. I had alignment done. I have problems when traveling over 65MPH. It begins with a very slight tremmor in steering wheel. Then at about 70 MPH, I get this faint hollow-echoing sound and the car feels like it is losing it weigh-ness (?). Then noise in front end. Also, have hard time keeping car going straight -- always correcting. Had tires re-balanced with no change. Took to highly recommended MB mechanic. He replaced upper control arm/joint and lower control arm bushings on left side. Also did lubed lt side suspension joints/parts. Re-aligned car but same problem. He fully checked rt side suspension and states all is o.k. No work/ck done to rear suspension. He is stumped and so am I. Any suggestions?