Amundsen control unit has its own speaker?

Just wondering if anyone knows about this... I was starting to set up my new Bit10 DSP controlled external amps system and the first step involves setting the input gains to the unit by playing a sine wave... with the RCAs for the amps pulled out. 

But I could still hear the sine wave! Very faint, coming from the front passenger side. I switched to music just in case there was some weird induction going on somewhere, or somehow I'd messed up the wiring - after all the amps are unplugged, so the speakers shouldn't be playing anything - and the music came through as well.

Turns out it wasn't the speakers in doors at all, it was actually coming from, as far as I could tell with my head stuck under the glovebox, the main processing unit in the glovebox.

So, does anyone know what's going on there?!