I've had a crossfire for about 12 years (04) that was about to die but being kept as a parts donor and just got another one (53) with about 80k on the clock and trying to fix a few small issues. One is battery drain that I never experienced with my previous model.

I'm aware of other threads suggesting multimeters and pulling all the fuses, but first a quick preliminary investigation I can hear a constant electrical noise even several minutes after the car is sleeping.

I opened the fuse box immediately next to the battery and for some reason at random decided to pull apart the one cable in the image attached and the noise immediately stopped. It may not be the cause of the drain, but I'm just curious to maybe start there before I spend a lot of time on it. Incidentally. My (factory) radio on this one works with no key in the ignition? Pretty sure that probably isn't right either and assuming that could be the next place to look. The alarm siren was already pulled by the previous owner on the assumption this was causing it.