Does anyone have one of these? I have the small plug-in one and when it runs it emmits a small high pitched humm. Kind of like...your ears ringing or like hearing electricity- I duno how to describe it. Anyway, roaches seem to be attracted to the room I have the plug-in in. Any else have these problems? And If they have a frequency that attracts them(roaches), is tehre a frequency that repels them? Could be a good invention!