ELTs go off all the time. If you hear one, report it to ATC or to the
police. They will send someone (probably the Civil Air Patrol) with
direction finding equipment to investigate. It is almost always a false
alarm. The most annoying one I can remember was an avionics repairman who
had loaded a defective ELT into a van and was driving around all over the
place -- to lunch, shopping, etc., before heading to the shop to repair it.
The thing would not shut off, and the technician didn't know it was on. CAP
guys were looking all over for it, "Now it is coming from over there..."