Inspiron 3471 unwanted beeps

This desktop is a recent purchase and it serves my needs pretty well. However, once it goes into sleep mode, it makes occasional random noises: beedle-de-boop, boodle-de-beep. It happens every few minutes with no recognizeable pattern for up to an hour, maybe longer. I think the noises might be signalling some background processes, but whatever they are, I can't find how to turn these unneeded noises off. Any suggestions? Thank you!