I’m not sure if this thread be closed or not. I’m doing a two cent wedge test. I sent this unit in twice and still get that hum and I was thinking yesterday to try put 2 copper pennies in. About 30 mints ago I decide to try it. Before I did this I tried the audio off setting tried each one hum comes and goes this is before the pennies try test. The black cover was a little tight to close i did manage to get closed not messing it up.