Could be the ignition switch and battery connections as Docjohn says. It could also be a short and what you heard was one of the larger fuses blowing (the energy released in blowing a small fuse would be minimal and probably inaudible) . In the main fuse box, check #9 (120 amps), and #12 (30 amps). In the main relay box, check #29 (50 amps). If any of these fuses are blown, do not attempt to fix by plugging in a new fuse. If one of these fuses is gone, you have a serious short circuit and will likely do more damage by doing a test re energization.