I have a beep and dont know why

I was taking my son to work and noticed I was beeping. It sounds like the door ajar beep but the door wasnt ajar. It was only doing it on the highway at aprox 65-70mph. It would stop when I slowed down but would start again once I got back up to speed.

All gauges were fine and no idiot lights on. She was running smooth. Anyone have an idea what this might be?

2006 Jeep Wrangler
4 cylinder
65,100 miles

Seatbelt alarm? Does it only happen when you have a passenger (then it could be the passenger side alarm).

Terry
2005 Wrangler - 31" tires on a 2" budget boost. Jeep deals (http://www.jeepdeals.net/)

No it did it to hubby when he was by himself and did it with me when I was taking my son to work. It did it that one day and hasnt done it again. I think I might have grimlins. It sounded exactly like the door ajar beep.