Amplifier draining car's battery

[KevinFX22]

I'm not sure if anyone else has had this problem, but my 2008 X type estate's battery began to give me problems that seemed to be down to its age. I replaced it and the new battery discharged over a period of 48 hours down to 2 volts. As I was hunting for what had to be something draining the power with the ignition off I heard a very faint buzzing noise coming from the area of the sat nav and multi changer in the rear wing that I had never heard before.  To cut a long story short, I've discovered that the amplifier is the culprit. When the ignition is turned off the amplifier still draws power. I've removed it and repositioned it so that I can unplug it when the car is not being used. We will see what happens, but when it is unplugged there seems to be no power drain.