The bluetooth is internal and connected with USB. But I can't find the make, model in your post so maybe I missed that. Without that I can't see if your machine has such internal USB devices.
After a few hours of being idle, my Vista machine starts making these USB sounds. Then a pop up appears near the system tray - One of the USB devices connected to this computer has malfunctioned and Windows does not recognize it.
I have no external USB devices connected to it. What is this?