Alarm Siren off while dialing to Monitoring Station

[evard]

Hi Expert,
We have an issue here when dialing to monitoring station, the alarm siren will off for 20 - 30 seconds, then back to on. In this moment, the keypad is hang and not accepting any command until the dialing completed.
When there is no dialing, the alarm siren works correctly. 
*The dialing is going through the community intercom line [using fiber]
Is there anything I can set to solve it? Or this issue is related to the fiber?
Thank you!

[slychiu]

The siren turning off while dialing to CMS is correct only for a few seconds while the dialing is going on
There is a possibiity that the electrical noise from the siren can affect the CMS transmission so the siren is turned off temporarily
The keypad is not affected, it does not hang. Please test again