alarm problem help needed

[lotusrock]

hi, i've got a alarm problem on 1998 uk 996 C2 started a few weeks ago and i've tried but can't fix it.

The alarm siren seems to go off for no apparent reason for a minute a a time then off but then straight off again. It's only the siren and not the flashers and the car can be started so the immobiliser is not getting activated. The only way to stop the alarm because the fob desn't turn the siren off is to take the negative battery lead off, however, normally you need the ignition on else the siren would go off but in this case without the key in the battery disconnection kills the siren. It's fine to drive and the siren doesn't go off when it's driven, and ocassionly i can set the alarm and it wouldn't go off for an hour or so. i've checked the normal doors, bonnet etc contacts and all seem ok and no obvious bleep as if something has been left open (have checked it open door and bleep does indicate open door). Checked radio on someone advice and seems ok, tried unplugging siren next to battery but backup siren which i think is the high tone horn still sounds. Someone also suggested locking and unlocking the car a few times then starting it up but seems to have no effect and not sure if there's a certain way of doing the locking and unlocking in a certain time frame. Tried looking through the workshop CD a have but 90 pages of alarm info and all dutch to me! can anyone help?

mike