Is the alarm constant or does the powersounder beep 3-4 times after locking the doors?
Just confirming
If this is constant try checking the bonnet alarm plunger maybe making bad contact when shut its either bolted to side of the PAS reservior or somewhere the other side of the engine bay. Position is dependent on whether facelift or pre facelift.
I'm not sure whether there is anything radio related regards the alarm, the only thing I can think of you may have knocked a cable behind there.
Still someone hopefully will be along to help you further
Good Luck in getting it sorted and welcome to the site