I also have an overly sensitive alarm. Mine is the stock alarm that came with the 2000 GTP, and when its out in the parking lot at work it often goes off if a trailer truck goes by, or a loud exhaust. I've set it off with my monte's exhaust too. It's pretty stupid how sensitive this thing is.
My work-around has been to lock the car once with the button, then press unlock once to unlock only the driver door, then manually lock the driver door and close it. This keeps the car locked without engaging the alarm.
If there is a way to adjust the stock alarm sensitivity, please share this knowledge! Thanks guys.