guys... I have a 2008 320d, E90 engine, 180k on the clock, full BMW service history. the car is used for a 150 mile daily commute. Have owned car from new. in last three weeks, having driven about 80 miles, car is parked up, and on returning to it some three hours later, it is totally dead- won't respond to either key, won't open, when opened manually, no response to key, no lights, no radio not even the red LED for the alarm. suspected dead battery, tried jump leads, no change.There appeared to be a very, very faint two tone from the immobiliser/alarm, barely audible inside the vehicle. On returning to car next morning (about 10 hours later ), opened with remote, and started first time. No issues while driving. local garage with up to date diagnostics can find no faults; happened twice more. last time car was parked overnight-had been ok when parked- but next morning, no response to key, same as before. Some hours later, started to work ok again. referred to BMW main dealer. They have had car for a week, can't replicate the fault, and diagnostics show no faults logged on ECU. Has anyone encountered this before?Has anyone any ideas where to look? my initial suspicion is a faulty immobiliser, but I don't know how the BMW system activates- does it normally shut the whole electrical system down?anyone any idea why the fault isn't being logged? HELP!!