2000 GMC Jimmy battery keeps going dead

My car stalled then all of a sudden it went dead the battery wont stay charged there is a weird noise coming from the fuse box under the hood also for the past month when I start the car it makes a backfire sound for under the hood. Also when the battery charges and I turn key the kight underhood goes out then when I turn it back it resets itself and goes back on and the security light comes on is there a way to disarm the security system