My Asko T700 Butterfly dryer is heating but really loud and clunky sounding. We're afraid to use it. The belt (if there is only one) appears to be intact.
The clunking is probably from the drum rollers. They are rubber, and disintegrate. I replaced mine a few months ago, I bought them online. You will have to remove the drum to get to them, you find find instructions for doing that on the web and replacing the rollers at: http://applianceguru.com/forum2/6940.html
You might also replace the drive belt while you are there to save another.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix tumble dryers.