Just worrying at the moment about an occilating drumming noise that is coming from my car atm. It has been getting steadily worse over the last 1000miles and is now fairly noticable, most so at about 30-40mph. Just wondering if anybody knew what it was.

I have checked all tyres and none have lumps etc on them, I was wondering if it was maybe coming from a diff.

It is a quattro car btw.

Thanks in advance.