Interim, I would suggest turning off the sound for "USB Connection/Disconnection" by going to; Control Panel > Sounds and Audio Devices > Sounds > Device Connect/Disconnect > then choose "(None)" for the sound. This will not solve your issue but stop the sound of USB but keeps all the other sounds available.
HP has an auto detect model for driver update option. Address;
http://welcome.hp.com/country/au/en/support.html
Most times it is the chipset driver has become corrupted or the mouse but as you said you have nothing USB plugged in. Do you get the visual notification in the lower right corner as well as the sound? If not, I would also try uninstalling all USB ports/Hubs in device manager and then Scan New Hardware and let Windows reinstall the USB drivers.
