Ive driven the car quite a few times since and everything appears normal now. (History: Following cam belt and water pump change on the Thursday afternoon I drove home about 3 miles from my normal garage. On the Friday morning at start up the rattle was evident so I returned to my normal garage and the mechanic told me it was the flywheel and I could see the engine vibration for myself. So I took it to another garage on his recommendation for verification and they road tested it. I left it with them overnight for them to cold start it the following morning and they could find nothing again.) As it's under warranty and as you've said a costly job. I want to solve this before the warranty expires. Any other ideas as to why its suddenly gone away?