If you are worried about getting caught by your boss, why not just leave the sounds disabled? Sounds aren't essential to chatting on IRC.
I do agree with the suggestion though. There could be an option to disable certain features (including sounds/flashing/etc) when mIRC is minimized. Perhaps with the option to choose when the features will be disabled (visible, minimized normally, minimized to tray, etc). Personally, I don't use sounds anyway, but it sounds like a useful (and easy to implement) feature.
-genius_at_work
