It's probably a bit late but thought I'd answer just in case anyone else has the same problem and needs a fix.
It's due to the "plastic fan" that pushes the air out through the vent warping, after a while and a fair bit of use the base of it warps and causes it to wobble and vibrate making a tremendous amount of noise after a while.
It's easy to replace and the part costs under £15 at the time of writing, you can get one here...
http://www.espares.co.uk/part/tumble-dryers/zanussi/td4112w/p/1088/332/0/553236/102940/plastic-fan.html
Be aware that if you don't fix it fairly soon after the problem develops it can cause other damage such as hitting and eventually snapping a plastic clip located next to it which holds an electrical component in place, this could potentially be very dangerous.
Hope this helps someone!
John Young, November 2008
