Sounds like the blower wheel is stripped out on your dryer.
It is a plastic wheel that is used to move the air in your dryer. It is stripped on were it goes on the motor shaft. It slips on the motor shaft when the dryer is running so it does not move as much air in the dryer as it should. This make drying a load of cloths take longer.
When the dryer shuts off the motor stops right away, but the stripped out blower wheel slips and spins free until it stops on it's own and that is the funny noise you are hearing at the end of the cycle.
It is number 4 on the diagram below.
Hope that helps..
Blower Wheel Assembly, part number: AP4294048