Strange Notification Sounds Invading our Space

My wife and I are laid up recovering from some medical issues and neither one of us want to get up much at all. So of course, now is the time when some mysterious tech notification chime keeps going off. Our main living area is a somewhat open floor plan, and it always sounds to us like it’s somewhere else. I was certain it’s not mine because I know my notification sounds; except I did recently update my Macbook to Big Sur, which probably changed some. She’s set with a Mac Mini and an Intel Nuk for one specific work application. I found the PC had updated and turned on all kinds of nonsense notifications, and cranked the usually silent volume up to 85%. I turned them all off, and pulled the volume back to zero.

Meanwhile, I grabbed my Macbook, which I usually keep the sound set to zero, and it was turned up for some reason. So was it my Macbook and some unfamiliar Big Sur sounds? We’ll see if all goes quiet now, or there’s something else going on, like a device in my daughter’s room, something a guest left upstairs, or another cause I haven’t guessed yet.