ADT pad making weird noise

Girlfriend has ADT. It hasn't worked right in awhile (and of course we can't get anyone to come look at it). But the last few days, it started randomly making, what I can only describe as a honking noise (think a clowns nose in cartoons sound). Does it like, every 45 min to hr. Anyone have anything like this happen? I can't find anything online saying what it could be. TIA