Another thought triggered by @Entz comments, I got a notification the other day to test Dolby stuff on Windows 10 for free for a while. You didn't perhaps turn something like that on and it is changing your sound?
Also some games have a settings in audio for headphones, or speakers, or surround, etc. Double-check none of those were changed by accident perhaps?
Along those lines a game patch could have changed the default sound profiles too.