Problems with USB connect/disconnect sounds are difficult to diagnose. I suggest the following:
1. Disconnect all USB devices, except for the keyboard and mouse, and see if the issue goes away; reconnect usb devices one at a time; if it occurs, you either have a defective driver or defective device; try doing an in-place Windows upgrade to replace the drivers with Windows provided ones.
2. Reconnect one usb device at a time and see if the error occurs; if it does it is probably a bad usb cable; this happens if the cable is pulled off often.
3. If you believe the usb cable is ok, the device is probably defective. Remove it and reinstall the remaining devices and listen for the connect/disconnect sound. If none, you found the issue.
4. Sometimes it could be a disk error; run a full disk chkdsk looking for errors; check the entire drive, including the unused portions.
5. I have had a bad memory stick present the same issue; run a memory diagnostic.