Noise-Cancellation Headphones, Ground Loop?, and MacBook Issues

[Hotspur71]

Hi,

Here's a strange thing: I've tried two different pairs of noise-cancellation headphones (Bose and Solitude) with my MacBook and with both a deep, but annoyingly loud, constant humming can be heard. This only happens when the MacBook is plugged in, not when it's running on battery. Also, it only happens when the noise-cancellation is switched ON; with regular headphones or if the n-c's off, everything is fine.

I suspect it's something to do with the MacBook's not being grounded with its two-prong MagSafe adapter and that there's a loop, but I'm not an audio expert by any means.

Does anybody have any kind of advice or can help fix this? It's driving me nuts. I've searched all over the Web and the forums for similar problems with the MacBook and noise-cancellation headphones but found nothing. It seems weird that it might only be my laptop.

Thanks for any advice you can provide.