I have some HD280's -- Great headphones, I really like em. Just the other day I was walking out of the library, through those metal detector type things, headphones plugged into my I-pod, no music playing, and I heard a very audible high pitched whine. I figure this is just some type of radio interference? Anybody care to elaborate?
Looks like you figured out out - I can't imagine why else it would do that. The tag detectors are RF-based.