black97legacy

I have a 97 Legacy 2.5 GT. My alarm system is posessed! The car locks and unlocks itself, lights flash and alarm sounded, until I took it back to the dealership for them to cut the wire so it would no longer sound (it was going off in my garage at 2:00 AM in the morning!). The only way to stop it completely now, is to disconnect the battery. I need to get this fixed because the battery keeps going dead. Has anyone had or heard of this problem before? Is it difficult to fix? What do you think it will cost? The dealership most likely will want to replace the computer module that controls the alarm system and they always charge a fortune to fix anything...no one else will touch it! Is that the only solution? Any information would be very helpful. Thanks!