Car alarm

car alarm goes off randomly, any time it feels like it. Always when parked and no one is in the vehicle. usually between 2 hours and 20 hours after shutting it off. sometimes after resetting it with the remote, it will resound within an hour and sometimes much longer and sometimes not at all. Of course, it almost always happens at night so I have left it unlocked many nights. I thought that maybe one of my neighbors had some new electronic appliance that might be setting it off, but no such luck. After reviewing multiple comments on the internet about this problem, I found that I’m not alone in this dilemma. Yesterday, I took apart the back hatch, exposed the mechanisms and lubed the electrical connections at the selinoids and the mechanical linkages. Remotely worked the locks 10 or more times to ensure free operation and even removed an old stainless steel sheet metal screw just laying inside the hatch next to the linkage. (obviously, the screw was not part of the original equip.). I thought; thats it, that could have been the whole problem. I Relocked the veh. with the remote as I normally do and no alarm went off until 10:30 this morning, when it resounded. ??? What a frustrating problem. Any Ideas to fix it?