What is the name of it?
I have no idea! I can just hear the unmount/mount sound.. I see no indication that something is suddenly not usable.. Is anything disappearing and reappearing in the My Computer window when this happens, such as built-in card readers or USB devices you have connected? What all USB devices do you have connected to your system?
I don't see anything specifically disappearing, that is what is strange.. I will open MyComputer and visually see if I can notice a change the next time it happens.. My USB devices are: wired mouse, wireless mouse, wired keyboard, wireless keyboard, wacom tablet, tvix.. I had this problem and I fixed it by running the Windows Startup Repair.
If you are doing work and it's annoying you you can turn the system sounds off in the sound controls.
I'll look into startup repair.. The sounds are annoying, but I hope I can find the problem and fix it (not just turn down the volume)!