The bleep is a Service Reminder Timer that has been set by your installing engineer. On earlier Accentas the reminder was by a flashing tamper light - on the G3 it was replaced (annoyingly) by a beep. Its not an exact science as it goes by the number of sets and unsets but is usually about a year from installation.
You would need to access the programming to reset the reminder timer. Unless you have the engineer code you will need to call in an engineer.
Alarm Engineer Bristol, November 2007