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Question: Some Niggling Doubts !!

Hi there...
I'm kinda zeroing on the AV40. However it would be great if someone here could help me out with a couple of concerns.
a) How do the AV40 hold up with the built in soundcards from Apple,(as I will be using these speakers mostly with my MacBook Pro.)??
b)I heard somewhere that there is a constant hum that eminates from the AV40s.Does it interfere with the sound output ??
Would be glad to hear from you folks before i bring home the box.
Thanx in advance