No ideas but I friend of mine almost crashed his altered a few weeks ago. The car started with a bounce similar to yours. He raced it that way for a couple of weeks. He wasn't susre what was causing the bounce. It got so bad on the last pass that I could see both sides of the car as it bounced back and forth in the shut down. He said all he thought was "OH NO, How bad is this going to hurt?" He was sure it was going to roll. It didn't. He loaded it up right then. He told me at the next race that the tires had went egg shaped.