I've ordered two different Panasonic HMC 150s for work use. Both have had the same problem -- even when I have the internal mic off and nothing/no mics plugged in to inputs 1 and 2 I still get a static noise when I record. If I have all of that off you would think if i recorded for 10 seconds and stopped and played it back I would hear nothing. instead i get this static sound playing back. Any idea what is causing that? or how i can fix it?