Whenever I use my built in mic, my volume lowers, then when I stop talking, it raises again on my computer. I've only noticed this with Windows Live Messenger, and thats because thats the only thing I use my mic for.
And a different problem: When I have windows media player going and I try to use my mic again in the previous instance, my mic wont even work all together. it just doesnt have any input at all. But wen i pause or stop windows media player, it will work again in the previous instance.