Worn out drum rollers could be the reason why your Whirlpool 29 inch electric dryer is making rumbling noises.
The dryer uses 2 roller on the back panel that the drum or tumbler rides on top of it. With time and the amount of usage these rollers wear out ant he dryer starts to make noises. These noises starts small and get bigger as these parts wear out.
To check and replace them you need to do the following. Disconnect the dryer from the wall outlet.
Remove the 2 screws under the lint filter and open the top panel.
Disconnect the door switch from the wire harness and remove the front panel. Then you need to disconnect the belt from motor and idler pulley. Remove the drum or tumbler.
Now you could see the 2 rollers. When they wear out you could see a pile of black metal shavings right under the roller.
The bushing inside of these parts is made of a softer metal than the spindle that it rides on it, so it wear the bushing instead of the spindle.
Remove the bad rollers and install the new ones. They are self lubricated and don't need to be greased.
Install the drum, the belt, the front panel, the door switch and top panel. Now try the dryer to see how it sounds now.
Watch the video below to see how this repair is done.
Below are the links to the parts needed for this repair.