have you re-inserting the cables and clean it up. Dirty wires could cause zzzz sound and for the bass, i think the subwoofer is already broken that's y the bass more powerful than before. In 1-3 months usage, (depends) both sattelites and subwoofer would break time by time.

Any setting you accidentally change in media player?

Hmmm i know what it likes when installing a webcam and also having a video-call. The master and wave will be decreased to 50% both.

But that doesn;t make sense, actually for me, wave 50%, wmp 50% and speaker 100%. So the master is somewhere 10-20% controlled using multimedia keyboard. If you set wmp and wave to 100%, the treble will become so sharp. Btw, try changing settings in media player especially equalizer and 'SRS WOW effect' (if available though).

My last suggestion, use wmp plus AC3Filter, it really makes a difference especially watching DVDs.

hmm for the soundcard, im using integrated, both laptop and desktop. So if youre using such X-Fi or Audigy, i cant help larh..
for wmp 10 or 11, i prefer :
techno as the equalizer (or Dance for heavier bass)
with the left option on first (set slider to move indenpendently).
SRS WOW:
I prefer 25% SRS and 50% WOW (sometime 25%)

But apart from it all i still use techno eq but i don't use SRS WOW anymore

I'm using AC3Filter instead.
If you're interested in this AC3, inform me after install and i'll share some of my opinion....

Good luck