I just bought a second ASW300 sub to add to my system, used, on eBay. It works fine, except - as the subject says - when in "auto" mode, after powering itself down, it makes a strange pulsing sound, with a slight chirp to it. It makes this sound even with no amp or speaker connected, and at all of the electric outlets I tried in my apartment. My other ASW300, bought new a few years ago, makes no such noise. Does anyone have any idea what it might be? I'm hoping there's a simple remedy, as returning it could be a pain. I can and will just use it without the auto power mode engaged, but I really like this feature... Anyway, thanks for looking and thanks in advance for any suggestions.