Update: I consulted a repair technician who said the buzzing was a sign that the starting relay/capacitor (which he referred to as the overload relay) might be the problem. He advised removing it and shaking it. If it rattled, it has failed. I haven't done that yet, but saw I could get the part for under $40, so I decided to order it and see if that fixes the problem. He said that if it isn't the starting device, I likely need a new compressor.

That makes no sense to me, since the unit would perfectly for hours on end, even days on end, then fail, and then go back to normal operation again after unplugging it for 20-30 minutes, Seems to me that if it was the compressor it would fail and stay failed, not work sporadically.

Any help out there?

Difficult to diagnose from afar. Replacing the relay is not expensive for a DIYer, and you're done if it fixes the problem.

Just to say ... an inverter and a start/overload relay are not the same thing.

Thanks, dadoes. I'm an electrician (power plants and transmission lines mostly) so I know the difference between an inverter and a relay. I just mentioned it because I found several posts referring to that particular part as an inverter, which I knew wasn't accurate. It's compressors and refrigerant that are a mystery to me! In my 40 years of experience I can't say I've ever heard of a relay that would work, then fail, then work again, over and over. But for $20 I'll give it a shot.

Hi OP, I have the exact same issues with the my fridge/freezer. Curious what ended up happening in your situation?