The air diffuser in my Kenmoore refrigerator makes a clicking (knocking or ratcheting) noise intermittently while the compressor and fan is running. The sound is at a rate of about 2 clicks/second and it lasts for about 20 seconds at a time. Then it will stop for a few minutes and do it again.

The temperatures in the refrigerator and freezer sections appear to be correct and balanced within each compartment, so there is no performance problem . . . just the noise.

Any clue what is causing the noise?