Have you ever taken a look at the "File Mappings" (via the Internet Control Panel)? Mine is a complete mess. Worst offender - Real Player - it grabs every sound/video/etc. extension possible, regardless of whether you tell it to or not. I see so many different file mappings for the ".mp3" extension it is ridiculous.
Is there any way to wipe/reset/revert them (without going in and deleting them one-by-one)?