Humming noise

[akkers5]

Sometimes when I park up and switch off engine after a drive, I hear a humming noise coming from the engine briefley, Then there is a brief crackling noise from behind the dashboard as though there is some insect in there.

I assumed it could be water gushing back or something. Any ideas?

[95JO]

My M235i does this too, I've heard that it's one of the ECU's shutting down, the one the controls the iDrive etc IIRC. No idea how accurate that information is, just that a lot of people with M135i/M235i and M140i/M240i report this and nobody has had any issues with it, so don't worry...