Just a quick thing to check, but you'd be surprised : Go into M&B's options and make sure the sound effects volume slider is fully to the right.
You can try setting disable_frequency_variation to 1 in the config file, that might help.
Something to check - in the surround mixer, CMSS and the advanced Equalisers (you know, hall, live, bathroom thing) should be turned off
If you have an onboard soundcard, make sure it has been disabled in the BIOS.
One thing it may be worth doing (if you haven't already) is going to Creative's site and use their autoupdate program. This will identify updates to more than just the drivers and allow you to download the relevant update.
Its also worth checking your speaker setup. Try switching to Mono and see if the noises are still missing.