Low Speed Rattle

Well, how many miles are on the car? Is it when you hit small bumps or at high speeds? If it sounds like a muffled bumping sound then it could be control arms. Notorious on the B5 A4s. My last one went through 3 sets in five years. I wouldn't worry about it being the timing belt, I've never heard of such a crazy thing. Your timing belt will give you little or no indication that it is going bad. But seriously, if you don't know the last time it was done, get it done. You want to do your timing belt like every 60-80,000 miles on a 1.8T. They are known to go bad prematurely. Not a cheap job though. Check behind but right above your wheel. There should be two arms that come together that you will see unless your car is lowered quite a bit. If you can play with them like squeeze them together or move them around they are bad. Could be the sound you are hearing.

As far as a rattle that actually gets faster as you go faster... brakes might need some changing with new rotors but you would feel that in the wheel. Do you feel anything in the steering wheel?

David, the issue was the timing belt tensioner was "fluttering" at lower engine speeds. It was only doing it at lower rpm's ( 1k - 1200 ) then started to get worse. With the interference motor didn't want to take the chance that it was the timing belt so changed them all. Timing belt, tensioner and water pump. The tensioner was so loose you could push it in and out of the housing with your fingers. Thanks/ Michael