how can i fix a tamper problem veritas r8?

hello i have a veritas r8 alarm and keypad its now started tampering a lot i could just be sitting in the house at next min you would hear this loud buzzing noise from the panel when i would stop the alarm and tamper would be lit up i had this fitted in 1996 dead on most of the time the tamper sign wouldnt be ligting up unset would just be lighting up green i have checked my sensors there ok ive stretched strings in the main panel and the rkp ive been up to the bell box it is a klaxon flashguard there was a spider in it i thought this could be making this tamper but wierdly just tapping the bellbox made the alarm tamper so i stretched the strings in the bell box tightend the screws and it just carried on ive switched the alarm off and the bell box starts to go off outside on battery backup ive tried everything could it be the battery ? anyone no what could be up with it ? thanks