If it is just the internal sounder, the chances are that it's a tampering problem. (This should be indicated on the display, or an LED will indicate either a "24 hr" or "tamper").
A tamper fault can be caused by loose connections in sensors, voltage spikes on power lines or bad connections in junction boxes. These sometimes have springy metal strips that are closed when the lid is replaced. Resolving the problem is basically a process of elimination, making one change at a time and seeing if stops the fault occurring.
Page 3 of this manual indicates how to deal with tamper faults: