When I start the car theres a thud. This does not happen each time. on 2004 Cadillac DeVille

This occurs after aproximately 10 starts. It makes the thud/metallic sound then its fine. I dont know if its the starter but someone suggested it may be that. Is that an expensive repair and can i avoid the dealership service costs.

Asked by for the 2004 Cadillac DeVille
could be starter or flywheel. styarter is costly do to location approx 600.00 flywhell is approx 1500.00 if needed
Thanks Greg. Does driving it with this problem do any further damage? Either repair is a huge cost and I would not want to add to the problem. I suppose as it worsens the thud will be more frequent.
if its the starter it could cause flywheel issues and u don't want that. have it ck'd soon