I have the HZ-370 electric heater, its making a beeping sound, a long solid beep, until I unplug it. Its not over heating cause I let it sit unplugged for 24 hours and it still did it. It doesn't matter if its turned on or not. sometimes it will run for a little bit and them do it. and sometimes it will do it as soon as I turn it on? anyone know what to do?