Volvo Repair: 99 s80 alarm, service mechanic, volvo dealer

Question
The problem started a month or so ago.
I lock the car with remote and leave.
Flashers go on and stay on. Anywhere from 1 minute to hours after I leave the car (random)
No one comes near the car. Once I tried to get the alarm to go off by rattling the doors, trunk, hood and shaking the car. No sign of sensitive alarm trigger.
Usually the alarm goes off when the lights do. Sounds quite weak. Not very loud.
Usually the light on the dash is flashing quickly, sometimes there is a message saying the alarm has been triggered.
Usually I come back and open the car with the remote and the alarm and flashers go off. A number of times I have returned and they did not stop flashing until I started the car. Today I returned and they did not go off (buzzer only this time-no flashers). I opened the car, locked, opened-started the car, off, started again and off. The alarm kept buzzing. I finally got out and opened the left rear door and the alarm stopped (that door was not ajar and I have tried to play with all doors to get the alarm to stop on previous occasions to no avail).
It seems as if the problem is getting worse.
My service mechanic just replaced the drivers door switch (which had other problems)-no change to the alarm (the alarm problem has been going on since before the door repair).
I have checked doors, hood and trunk latches-no obvious problems except the trunk latch was loose. I tightened the bolts and the alarm problem still exists.
I did have a problem with the skylight recently. This seems to be connected in some way according to emails I have seen on this site. It will open but the tilt mechanism will not work.
The mechanic had it apart but could not find anything wrong.
The mechanic by the way is a licensed volvo technician but doesn't work for a volvo dealer. He cannot find a code in his computer to explain the alarm problem.
As a last resort, can I disable the alarm?  

Answer
Well unless your volvo mechanic has the latest volvo diagnostic computer he is not going to be able to get any codes.  Also he would have to have worked on volvos at the dealer at least up to 2001 to have any history with this problem.  If you replace the siren it should fix your problem.  It is under the fender liner on the front right.  fairly easy to do and that should stop all these hassles.

James