Loud rumbling sound

I have a maytag dependable care plus/ heavy duty dryer and it has been making a loud noise when I use it. It is like a loud rumbling noise and it has been doing it for about a month now. It takes a long time to dry clothes and I was wondering what was the problem

If you turn on the dryer, and let it run for thirty seconds, and then shut it off. If you hear that rumbling for a few seconds longer after the dryer has shut off, the motor blower whelll is broken. If not, it would be the drum rollers. Tom http://www.applianceeducator.com/parts.htm

Thank you very much