Thanks for the replies. Since the doors at the convenience store are manual, there's no chance of interference from them. Also, I conducted a very limited test this morning stopping at a couple of church parking lots about a quarter mile from the store. I had trouble with the Smart Key system at both places and I was parked far away from any buildings.

My guess is that the radio towers (or whatever they are) are putting out enough of whatever they put out to cause the interference with the Smart Key system. I'm just glad I don't live near them.

Unfortunately, there isn't another convenience store that's convenient so I guess I'll just have to live with it.