I have recently had my rns-e navigation unit stolen from my Audi A3. I refuse to pay £600 for a new one so I have installed an aftermarket radio. I purchased an adapted for the unit so it works with the Audi quad lock adapted. Now the radio and everything works fine the problem I have is when I take the key out of the ignition and the radio powers off static noise comes through the bose speakers. When I power the radio back up the noise then disappears. On the back of the radio when I unplug the amp cable this also stops the static noise.

I was wondering if anyone knows what may be causing this problem and how can I fix it. Any suggestions would be greatly appreciated.

System:
Full Bose amplified system
Pioneer Bluetooth radio with s/w ctrl
T1 audio adapted + pioneer patch lead with s/w control.

Kind regards.