I searched the archives and I can't believe no one has mentioned this yet! This is a huge problem on both my Rev A and my new Rev B. When you connect an external monitor and external speakers using the headphone output, there is a high frequency ringing sound coming out of the speakers. I've managed to live with it by turning the treble to minimum and keeping the volume low enough but at the expense of sound quality. The strange part is, if you disconnect the monitor, the ringing sound stops. The problem only occurs if you have speakers and monitor plugged in at the same time. I've tried this on my Samsung monitor, my SONY TV, and my Panasonic audio receiver. The problem occurs with both Rev A and Rev B while my white MacBook and 2007 MacBook Pro all sound fine. My theory is that because the ports are packed in so close, the audio output is getting interference from the Mini Display/Micro-DVI port. Is there anyone who is not experiencing this?