My refrigerator just today started periodically humming for about 10-15 seconds every 20 minutes or so (something low, 1kHz or lower, I'd wager, though I don't have an amazing ear), followed by a quiet pop.
It has never done this before. Where should I start looking, and what can I do to diagnose this?
The refrigerator is a Kenmore Coldspot (59592990). And no, the icemaker is not on. The noise appears to be coming from the rear of the fridge.