The fridge/freezer (it's a side by side jobby) at work sporadically hums. Checked the shelves, door, contents - all the usual suspects and nothing appears loose.
It'll be quiet for ages, then hums for a while, stops, hums..you get the idea, although it's not a rhythmic stop-start.
So, short of teaching it the words, what's the most likely cause and best cure?