The shaded pole motor inside your Payne furnace has a very low starting torque. If the bearings are starting to stick, the furnace will heat up and start to burn the dust inside the furnace. The thermal switch should shut the furnace off at this point. Because of the low starting torque, the motor may run sometimes but not at other times. To check, reach inside and give the blower fan a shove. It should spin freely. Otherwise, take the motor out, check the bearings, oil or replace as necessary.