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This question comes up quite a lot. Have you tried searching the forums?
 
Do you have the iTunes widget running?

This is a good call. There is an abundance of 3rd party widgets hosted on or off apple.com that will randomly start iTunes. These widgets don't even have to be iTunes related. I had a TV Guide widget that randomly started iTunes.

I would deffinitely check out your 3rd party widgets if you have any.
 
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