This is really beginning to irritate me. I don't know if its specific to WoW but that's when I notice it the most. I could swear I've noticed it before during DVD playback too. Basically when a loud sound happens, such as an msn message arriving, all other sounds go much quieter and then slowly come back. In WoW the background noises go really quiet and then slowly get louder again. Its like its attempting to normalise (something I despise) the volume. Any ideas? I'm sure there must be a simple fix somewhere!