strange beeping sound while driving.

[mapleridge818]

I've had my L400 (gasser) for about a month now, and while driving it makes a strange beeping sound inside the cabin. It only happens when the vehicle is in motion. It's a fairly faint beeping, and it's really hard to tell where it's coming from. I thought it might be related to the stereo, but I've installed a new deck, and it's still there.
It starts slow, (maybe a beep every 2 seconds) and slowly increases in tempo (up to about 3 or 4 beeps a second) and then slows down, and goes away. It has nothing to do with vehicle speed, as it does it at low speeds, high speeds and everything in between. It also doesn't seem to do it all the time.
I know this is a weird problem, but thought maybe someone else has had this before and figured out what it was.

[Mr. Flibble]

There is a reversing beep, but I am guessing it is not that.

I had one of my dogs cause a really strange beeping noise by standing on the passenger heater controls behind me while I drove. Took me forever to figure out it was him stepping on the controls with his paws.

More likely, it is some after market add on that the people put in. I would say turbo timer, but you have the V6, so it isn't that.