Diagnosis
The turntable motor gearbox is failing or the roller guide and support ring are misaligned. A broken plastic gear inside the motor causes clicking.
How to Fix It
Remove the glass tray and support ring. Clean the cavity floor and the roller guide. Ensure the support ring is seated correctly on the roller guide and the hub in the center. The ring should rotate freely by hand without catching.
If That Didn't Work
The turntable motor under the cavity floor has failed. Listen near the center of the cavity floor for the click. The motor assembly must be accessed from below after removing the outer cover and base plate.
Heads Up
Do not operate the microwave with a stuck or clicking turntable. Uneven heating and damage to the motor can occur. Remove the tray and ring for manual rotation of food during cooking as a temporary measure.