This can happen for various reasons - power supply not providing enough power for some device (especially if you are stressing your hardware during playing games or folding), motherboard going bad or shortening out somewhere, some PCI/PCIe card not being seated in properly, some USB device going bad, etc. Good luck trying to figure this out!
John, your post made me think of something to check on. Time to crawl under the desk!EDIT
: So far so good. Earlier this afternoon, I was digging around. Needed to plug a new USB hub into a pre-existing hub. The new one has rocker switches for each USB device, and I wanted to put some of my music devices on that new hub, so that I could switch them on and off without using the switch on the device itself or having to manually plug/unplug the USB cable. Yuck!
Native Instruments bus-powered devices are notorious for not even having power switches, so the USB ports get heavy use if you're like me and prefer not to power them when you are not using them.
Yeah, I know I'm running a risk plugging hubs into hubs, but in my home office/studio, the computer is in the middle and already has long USB runs out to the perimeters. Not much I can do about that...
Anyway, once I plugged the errant free-dangling power supply into its hub, the sound seems to have stopped. I probably won't be 100% confident unless it stops happening for at least a couple hours.Edit 2
: By the way, I did notice that Device Manager seemed to blink TWICE with each disconnect sound. I suspect that one was the disconnect sound, followed by a successful reconnect but no accompanying sound. It may also be plausible that the new hub, though it was itself plugged into AC power and not powering any devices, may have been causing a draw on the unpowered hub, bringing it occasionally too low (on bus-power alone) to maintain communications with Windows. It would disconnect, then immediately reconnect. And a few minutes later would do the same thing all over again.