Had my MR2 Turbo stored during winter. I even put styrofoam blocks under the wheels. However the ones I put under the rear wheels were quite hard and didnt really flex.

Now I've got a vibration from the rear at 50 - 65 mph. Under and over that it's absolutely fine. Can't tell if the problem existed last season since one of my wheels was buckled. Car is on 100% straight and balanced wheels now.

Any ideas how to get rid of the problem without buying new tyres?