Hi, I just bought a 230 SLK and it started to make a howl or whistle on occasion. Comes and goes, I really can't tell where it is originating from, sounds like under the shifter but can't imagine. I was thinking wheel bearing but I read a post about a changeover valve, so now I am not sure. Mine only makes the noise when driving so don't think a changover valve. Anyone ever have similar? Anything else that could make that noise?