2004 making a whooping noise

We have a new 2004 Venture. We are going to have the dealer take a look at this problem soon, because it's still under warranty obviously, but I'd figure if I can help them out it won't take them as much time. Basically when we are driving there is the occasionally whooping sound, we think it is coming from the back. It sounds kind of like a police siren starting up and is a whooooop. It only happens for a second or two each time, but is rather annoying. Any ideas? Thanks

Does your Venture have the optional air compressor in the back? It keeps the air shocks pumped up, and runs occasionally, but doesn't make much noise. I've not noticed mine during driving, but only when parked, when in makes a low pumping sound. It shouldn't sound like a siren.

I do not have the optional air compressor in the back, nor the automatic load leveling feature so it is not either of those. It's almost a car alarm is starting to go off or something, and then shuts off. I'm not aware of any alarm in this vehicle. It is a LS with the standard package.