Clicking sound from inside fuse pannel when starting and turning car off. 2008 mini

as garybee says welcome gary,cars these days have a central ecu that controls everything on the car and stays awake for 3 minutes after you switch off and lock the doors they a central relay within switches off and at that point only a 100-400miliamps should be showing on a amos draw test, ie hook test meter set to amps and across the live feed battery cable to its battery terminal as to read the amps drawn, like after 3 minutes with all doors closed and car locked by key fob it should sleep,,, if like yours have 3=4 amps drawn at this point then i use a fuse holder tool amp tool ie plug it in to each fuse holder and read the draw until find the one with the high draw sometimes its that easy, in other cases its not as if fault is within the bcm you can have a number of circuits all reading 1amp say ie 4 circuits then its a hard one and could be some many things very common is short circuits where wiring has got wet common on cars that leak also under bonnet wiring gets wet and salt off the road will cause a acidic reaction that plays hell with things,, process helps, ie i do scan can for fault codes get a idea to where to start maybe, then its multimeter searching as above for power ie amps,
would also check the alternator output and if have a draw at battery try disconnecting it see if it goes away very common for diode in there to fail and discharge both directions,