I can also remember reading (somewhere) that the TCH performs some sort of function hours after it is shut off. Something like 8 hours. I think it has to do with purging the evaporative system (not confident on that) but I have heard this process when I've been in the garage and thought the car was haunted. It sounds like a pump running but only for 10 seconds or so with my car.
Are there other functions that run periodically even when the car is off?
I would THINK this would be something powered off the main inverter and therefore not something that would draw off the 12volt battery but who knows.
If this process got "stuck" ...
??