veritas r8 sounding when light is on ?

hi i have a veritas r8 with two panels upstairs and downstairs and the main panel in my celler it has been in for 11 years lately its been tampering only when i switch the celler light on its a flourecent fitting right next to the box when the light isnt on theres nothing rong with it and the tamper light goes off. in the main panel it says texecom 1996 and there was a spider in there which i removed and there was no loose wires i even took the battery out and still did it so i put it the battery back in the panel and screwed it up and the battery works fine and also noticed if you leave the light on the tamper light comes on then goes off then later comes on again but when the lights off it dosent tamper at all PLEASE HELP