RM6750 sub: rumble with no input connected

[Marquis]

I have a brand new RM6750 sub that is making an uneven rumbling noise (sounds like thunder) when I plug it in, with no input connected. Even when the power is set to "auto", the green light is on and I can hear the noise. I tried different circuits in the house, including a circuit that has nothing on it but a single GFI outlet, and I have the same result.

[Schwingding]

You're going to have to return it. Sorry.