Hey dtjs,
I must say; that looks distinctly aftermarket.
For two or three reasons.
Firstly, the mounting lugs look they are meant for 'any surface' rather than a particular position within a car meant to hold the unit.
Secondly, it looks like the easiest place in the world to have attempted to hide something, and I don't really see any signs of failed fixings.
Thirdly, you don't see a lot of heat shrunk AMP-superseal connectors used internally within vehicles; the thing looks like it's built for an underbonnet mounting. (Although, upon reflection; they seem a bit square to be Superseals)
Does your car have an aftermarket alarm, hands free phone-kit, or 'significant' stereo??
Can you get an image of the other side?