The rumble may be the sound of the drum dragging against the heater housing. The rear bearing may be trying to dig it's way to china. The slides are also probably shot and now you have metal to metal on the front of the drum. To access this dryers innards you need to remove the 4 torx bit screws in the upper doorway that hold down the top. Then you can access the screws that hold the front on. Then you can remove the front. Next you need to get the drum out. remove the rear panel and take the idler loose. remove the drum and inspect the rear hanger bearing and the front slides. If you let this go it could ruin the heater element or the drum and start cutting the clothes.or both.