High pitched sound during games

My system info:
Windows XP
Socket 939 Nvidia Nforce4 motherboard
Viewsonic VA1912w monitor
Geforce 6600GT video card
Sound Blaster Live (ancient video card)

The problem i get is a very high pitched constant squeel coming from my computer case. This problem only happens during games randomly after about a minute. The only way to stop it is to exit the game or alt tab out. After a second the sound goes away and then i can alt tab back into the game from whence the problem will start again in about another minute.

The problem started occuring after i replaced my old monitor with my new widescreen one. The sound problem does not happen any other time other than during games. Previously it was only happending during games on the UT engine and i was able to fix this temporarily by (chance?) disabling all hardware acceleration for my sound card. Now however it happens during all games as before again.

I can't find anything about this sort of problem and have no idea what could be causing it.