How can I stop the alarm beeping on my optima compact security system?

I have an Optima Compact security system approx 8 years old which has developed a fault. The external box starts beeping when alarm is in both the day mode (turned off) and in the system armed mode. Entering the user code will not turn off the beeping. I have renewed the battery but the problem still exists. The fault also exists when the system is in the engineering programming mode. Can anyone help with a diagnosis?