antsnaith

have a feeling it maybe due to having swapped out the OEM radio with an aftermarket one?  any thoughts or how I solve?

Hey all, 
I have a 1999 Boxster S.  For some reason, whenever I lock the car the alarm sounds every time (Horn and beeping).  Sometimes within 10 mins, other times it will activate overnight.

Does anyone have any idea as to why this may be happening?  Battery issue maybe? 

As it is, I cannot now rely on locking the doors on the car as it either embarrasses me whilst at work or shopping, or wakes me up in the middle of the night!