JVM1540 Over range microwave turntable

Question

The turntable of my one-year-old JVM1540 over-the-range microwave continues to run after the cooking timer has ended. It stops when the door is open, and usually after a few minutes of leaving the door ajar, I'll hear a slight click and know that it's "safe" to close the door again. Sometimes it takes longer than other times. What causes this? How can I fix it?

Thanks for any help!