When I cold start my car I am getting a lot of tappit rattle. I don't think they are worn because it's getting noisier too quickly. I know the oil is well overdue for a change and suspect this is the problem. What is the best way to ensure the tappits are cleaned out before I change the oil? I'd prefer not to have to remove them, but will if necessary. What's the best oil to use in a C20LET?