Downright dangerous.?
You sure he is an Electrician??????
These are suseptable to vibration, tighten up the mounting screws and or aback fixings adjusting the back fixings so there is slight tension on the control panel back, either of these will work.
As your your brainy mate tell him about generated heat in a non vented space ( As it virtually is) and fire hazards. We now don`t even leave paperwork in the panels let alone bog roll.
PS 18 years, when was it last serviced had a battery change? 5 yrs is the max before you should change the battery (7ah just google 12vdc 7ah alarm battery) this may be overloading the transformer also and causing the hum.
Next time before guessing, give us a call :D
Alarm
July 2012