Is it allowed to wash one's car during the 9 days?
Or is it like clothing, since it is also for show and it surrounds you?
This article says that one may wash his car and polish silver, but not shampoo the rug. It does not give a reason. Then, again, I would assume regarding Nine Days that if something is not specifically mentioned as being forbidden, then it's permitted. Kudos to Alex for the M.Y. link.