Weird coughing sound!

I'm getting an occasional fairly quiet sound from my Mac. It's difficult to describe, but it sounds like someone coughing in the distance - in fact for a while I thought it was our next door neighbour! It's quite random and I can't tell if it's coming from the speakers or from the internals of something. Does anyone recognise what this could be?

Setup is M1 MacBook Air connected to a Studio Display with two external drives also connected to the Display. I previously had an iMac and never heard this before.

Thanks.