Subwoofer output connection wire

[Wconley]

We have recently purchased a 2009 27fB Signature. The previous owner replaced the original stereo (I think) with a Sony head unit with DVD playback. Additionally they installed a Sony CD changer and two Direct TV receivers.

When we watch a movie through the Sony the subwoofer makes random noises almost as if it were playing LF sounds from another audio source. I pulled the radio head unit out of the overhead and sound the subwoofer output unconnected with its protective cover in place.

Does Airstream connect the subwoofer directly to the head unit or do they connect through an external low pass filter split from the speaker outputs?

Any idea why the subwoofer would be making extraneous noises?

Thanks in advance.