I was in St. Augustine two weeks ago. I have had this annoying ticking or knocking noise for a long time. Anyway while I was there I pulled into a Mercedes garage a small independent shop. I asked the guy what it was. He said it was the vacuum pump. He said it was worn out and was causing this annoying ticking. He said he had changed many of them because of this. I will soon be changing mine.

My 2 cents

Dieselman