My experience is similar to yours. I stopped at Denny's restaurant at dusk. I pressed the door lock and the beeper continued as I closed the door. I saw no lamp lit on the power button looking though the window. I pulled the back door handle and it was locked. I figured i'm ok and went inside. I think the MFD display was dark. The car beeper was off when I got back in to drive off.

There is a large cell tower a few hundred feet behind Denny's. It's loaded with small antenna's and includes two good sized microwave dishes.

The other location is at the new Walgreens. I have the same beep as I get out and close the drivers door. Could be the Walgreen's door sensor is adjusted too high.

I have the same problem at a particular convenience store in the north part of town.

This convenience store has a large cell tower close behind the store.

I never have any beeping when I turn off the car, lock the door and close it for the night here at the house. We live 8 miles south of town. No strong interference out here that I know of.

If it is interference maybe someday they will come up with a small receiver with a green, yellow and red led signal strength indicator in the dash alerting us of any nearby signal that would mess up our keyless entry receiver.

Actually I have not worried with this as the car seemed fine when I returned to drive off. Just thought I might add my theory to your thread.