Something weird happened. About 3 days ago, I put the DVD with the windows 7 installation in my DVD ROM drive, left it in there for several hours... and the problem with the buzzing sound during media playback disappeared on its own.
How could this be? Unless Windows "knew" what it needed to find on the installation disc, I can't see how it could fix this issue?
I didn't start the repair procedure (yet). I don't know if the System Restore issue is now resolved as well.