Each time I start my car, I hear a loud clunk and can feel it through my steering whee. The clunk is so strong that it shakes my car. Sometimes when the engine is still hot, there is no clunk or a minimal clunk. Otherwise, my 1988 Volvo 240 runs perfectly. Could this merely be motor mounts? Upon starting, the engine doesn't appear move any more than during its normal running. Has anyone else experienced this?