Hi, I think the bell you hear is the pressurization's bell. It advises you for a pressurization's problem. You must pressurize the cabin before take-off. For doing this, below packs, below APU you'll find two displays: the first for maximum altitude you are going to reach and the second for minimum approaching altitude. (for example: 35000 - first display - 2000 second display below)
If you forget to do this for conttinuing the flight without prooblems, go down below 15.000 ft. The bell off and no problem to crew and passengers. Otherwise maybe you'll se all black.