is an odd thing, but the trunk light is in circuit for trunk switch, and is tied into the factory alarm. check the trunk light for arcing on the frame that it is mounted into, as this can cause alarm to go off. you could just pull it down out of trunk roof, and wrap electrical tape around it and connector to make sure there is no metal to wire/terminal contact. this may not be the problem, but one i saw that ran me for a big loop. when it came into the shop, hooked up the scanner and the alarm history was clear. through further diagnosis found the module was faulty, but after replacement, alarm would still go off. but new module would tell me what was setting off alarm, so went through and found the trunk light would sometimes arc and set it off. sorry for long winded post, but check this out along with the doors and such as mike suggested.