Don't know if this is your issue, but . . . I have a 94 Camry with apx. 140k miles. Obviously didn't happen too often, but found violent shaking under acceleration at higher speeds - like over 85 mph. Kind of like something was bouncing up and down but I couldn't really tell just where it originated. Then discovered a crack in the passenger side drive axle rubber CV outer boot, so I purchased a Toyota remanufactured axle assembly. (fortunately my online guy gave me the right part number and the local dealer matched the price - the local dealer had given the part number off by one digit - axle fit yr. 2000 Solara) Anyway, the factory service manual shows some "non-reusable" parts, that should be replaced. There's a diagram with a symbol for those. One is the snap ring, another is the center bearing lock bolt, and also the cotter pins. A prior mechanic had replaced the boots once already for the prior owner, and I found the cotter pin for the tie rod end had been reused, so I'm quite sure the snap ring was reused. Dealer got $20 for the snap ring from me, but I follow the instructions in the book. Main point of all this is that the center bearing lock bolt hadn't been replaced either. Had read many accounts of difficulty in removing the axle when the center bearing hangs up in the carrier. Fortunately mine slid right out, however that lock bolt is a special bolt. There is a neoprene rubber tip apx. 1/4" long at the end of the bolt that holds the center bearing from turning in the cast iron carrier "locking" it in place. The locking bolt I removed had that neoprene tip entirely missing. Undoubtedly the extra part wasn't supplied, and the mechanic didn't want to delay the work to the customer for something "minor" like that. So I imagine, it is entirely possible that center bearing was rotating in the carrier with some clearance and flopping up an down slightly under load at higher speeds, setting up an oscillation along the length of the axle. The passenger axle is long enough and heavy enough to create some vibration.