My 2.0 TDI has developed a squeak and vibration when ticking over? The crazy thing is this disappears when I switch on the heated rear window????????? Or the heating?????? I have looked for loose components in the engine bay but I have found nothing! This is a horrible sound, you know, the one that really annoys you. I had someone look at it and their diagnosis was that the alternator pre-tensioner needed replacement, so I purchase one from the stealers, had it fitted, still the same! Any help advice would be great, Thanks in advance.