I tried doing a search, to see if anyone has mentioned this before, but didn't find anything. I have heard a high pitched beep, which doesn't seem to emanate from the audio system. I haven't been able to pin-point where it's coming from, or conditions under which I hear it, but I will try to gather more information and post here again. But, I thought it might be worth asking here. My boyfriend doesn't hear it, but I think that must just be the frequency. It doesn't happen all the time, but when I hear it, I will hear it a couple of times a minute.