For a couple of weeks, the Windows 7 Sound dialog box (the one with all the Playback/Recording, etc options under Control Panel-Hardware and Sound) has been randomly opening. I'll close it and at some later time it will spontaneously reopen, although unpredictably.
The OS is the 32-bit version of Windows 7 Home Premium running on an HP Pavilion Slimline s3330f that we've had for a couple of years prior to the emergence of this issue.
Unfortunately the system restore points don't go back far enough to try that option.