Lately my dryer has begun making a vrrrrm, vrrrrrm, vrrrrm sound. It only happens when the dryer is warmed up (i.e. after running for 10 minutes or so). If stopped and re-started, the sound begins almost immediately, and there's a kind of metallic sound as the drum begins spinning on restart that's not present when starting from cold.

In the past (using help from these forums), I've replaced the felt seal, the rear bearing, and the heating element (all within the last year); when this sound began, I opened up the dryer and inspected the ball joint (which looked good--when it needed replacement it was nearly worn flat; I added some more of the lubricant that I had left over from that repair, but it didn't change anything).

The dryer heats up fine, and clothes do come out dry, but it seems like things are taking a bit longer than usual -- it almost appear as if things aren't "tumbling" as well (i.e. if I open the dryer clothes are up against the walls of the drum and the fins, whereas if I remember correctly it used to keep the clothes lifting up and falling down.

Any suggestions as to what might be the culprit here? The belt?

Thanks!

Matthew