You might find the bang was the aircon system bursting. A pipe or a joint.

Similar thing happened to mine a few weeks ago...

Had the aircon on and parked the car up, when i started the car back up about 20 mins later the aircon was still on and there was a big bang and a smoke like vapour surrounded the car. Im assuming it was the aircon system blowing up but i just carried on driving and havent even tried to see if its working, too scared incase i have to go back the dealer.

If you do go to the dealer take a spare pair of trousers with you as they have your pants off!