This would be better posted in Plumbing, but here goes anyway.
If there is water coming in continuously, and there are two pumps, most likely the lead pump has failed, and the alarm goes on until the lag pump has lowered the sump level.
The control logic might also sound the alarm when the lead pump is called for, but does not respond. The alarm is sounded for 10 seconds, then the lag pump starts.
Just two possibilities, with more info, we could be more helpful. How many pumps? How many floats? Age of system. Type of control.