I have the same problem in mine. I have a Neptune front load gas dryer, and believe to have narrowed down the problem to a noisy idler pulley wheel. You'll have to remove the from cover and look into the unit while its tumbling, I put mine in cooldown mode, so the burner doesn't ignite and hold the front button in so it will start, then I can view and hear whats causing the noise. Now that I have found this - I'm trying to find the best way to get access to this part so that I can replace it by removing as little as possible. I have been searching the web to find how to remove the covers but cannot find anything decent. I hope this helps you.
Rudy, December 2006