We have an NEC Electra Elite IPK with a DPH board and 3 Door intercoms. One of those intercoms keeps calling the phones around the same time every night. We've swapped out the intercom in question, checked wiring for any shorts and swapped out the DPH board as well, but the issue persists. Does anyone have any suggestions?

OK this may seem silly but I would set up a camera of some sort. I had the same issue a while back and after 3 mos we found that a squirrel would climb down on the unit and inadvertently set off the door call button. this would happen about once a night because when someone would go out the door to check it scarred the critter away. we found that employees were leaving food out there for the squirrels.