I've noticed that lots of people have this problem... that's why i love wmp...

I've searched the web and i can suggest you try this possible solutions (choose one):

1.- Change your sound settings to 16 bit instead of 24 bit in quicktime, should fix it...
2.- Set rate to 196khz and size to 24 bits. With this setting, even while playing the cpu hog it get no audio distortions.
3.- Set the volume control (from iTunes7) to its maximum
4.- Open up Task Manager, and find iTunes on the "Processes" tab. Right-Click on it and select "Set Priority". Change it to "Above Normal". Check and see if that works for you.

Try if this works, i don't really use itunes (only for converting songs)

Taken from:

here
and here


P.S.: If nothing works, why don't you just rollback to itunes 6?

Damn, the second link doesn't works, whats wrong with hyperlinks. Whatever:
www.neowin.net/forum/index.php?showtopic=495424&view=getnewpost

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