Not all the time, but about once a week I'll walk to my car, press the unlock button, and nothing. This happens on a weekly basis for reasons I can't figure out. So I have to manually unlock the door, start the car and let the system recognize the key fob again. I've tried a search but nothing came up. The batteries are fresh, so that's not it, and the key fob is tight, so I doubt the batteries are loose in there.

What could be the issue?