Aftermarket radio battery drain

I have been getting a battery drain issue from an aftermarket radio, vehicle electrics companies have told me the can bus adapter with the igition off and key removed is still actively switching something on and off pulling upto 1/4 amp.

I have an Audi A3 2010 with fully amped Bose sound everthing works fine accept this battery drain issue which will drain my heavy duty start/stop battery over 2-3 days.

I have had the main battery wire cut and a relay switch installed connected to the blue amp on wire to the head unit after reading that similar VW cars monsoon amps have a permanent live which switches the amp on when sensing voltage from speakers, this hasn't worked.

I've also bought a replacement can bus adapter, still no help.

I am thinking now to isolate any non igition power going to the can bus adapter as when I detatch this I don't seem to get battery drain. Does anyone know if I was to cut the thin yellow wire leading into the can bus adapter and wire to a switched live at the fuse box would this solve the problem. This yellow wire splits from a thicker yellow wire into the head unit. I'm thinking yellow as this is usually a permanent battery live

Thanks for any advice