2004 Ford Freestar van alarm issues
 

I have a 2004 Ford Freestar cargo van. Recently is has developed an annoying problem. While going down the road an alarm will sound off about every 25 to 30 minutes. Sounds very much like the Door Ajar alarm ( five sets of five beeps in a row) then it stops for another 25 to 30 minutes, then sounds again. No lights are lighting up on the dash to show what the alarm is for. Yet all the lights on the dash seem to light up as supposed to when starting the vehicle including the door ajar light. And if you open any door, the door ajar light comes on.
This has me thinking it is not a door ajar issue but, the alarm does sound very similar to the alarm you get if yo move the vehicle with a door not secured. The van has just under 150,000 miles on it (actually about 149,000. Any ideas?
Thanks for any thoughts.

Do you have the seat belt connected , in place for driving?

Yes the seay belt is connected and the alarm sound is different than a seat belt alarm.

Since there a few alarms that don't quite sound the same, can you compare the alarm you don't want to one of the alarms the vehicle provides and maybe we can get an idea of which system is sending it?

Key left in ign
lights left on
seat belt
Owner's manual list?

It sounds like the "door ajar" alarm five approximately 1 second long Beeps with about a second in between each. About six second delay before the next set of five starts. It repeats this five times and then stops for about 25 minutes before doing the whole process again.

The seat belt alarm sounds like someone ringing a bell. More of a ding, ding, ding in fast succession for several seconds. The alarm i'm hearing is definitely not the seat belt alarm. The lights left on alarm would be closer to the seat belt "dinging" only just a bit longer between the dings. The alarm I am hearing is definitely not the lights left on alarm.