This is usually a bad ons port relay issue
How would I identify which ONS port relay is assigned to a specific phone number / room?
Each port/ext has it's own relay... They sometimes go bad and sort of "flutter" which can cause it to look like a pulse dial to the system and the proper sequence of pulses will trigger a 911 dial event. The key is to deprogram that port so it isn't capable of dialing or physically replace the station card.
If this is happening, look at the maintenance log for which extension is causing the issue (it will generate 911 alarms) and you can either move it to another port or replace the station card.
Sometimes even just dust buildup can cause this... I have cleaned systems out with compressed air and had this issue go away, but there is no guarantee it will work. This is generally only on the old 12-port ONS cards in the 96-port cabinets only though (the ones that use the 8 interface cards and a BCC card).
