Sounds like I have the same little squeak joe_black. It started about 24 hours after I got mine and it comes and goes. I can be driving along and not hear it for hours and then all of a sudden it comes back and is loader then ever. I've tried almost everything to get it to go away with nothing working. It originally started on the back passenger side and now its migrated to both back's and the driver front.

I'm guessing it might be one of the following, shocks, springs, bushing or even the bolts on the rims.

Another thing I've noticed is that I can reproduce the issue by "pushing" the car at an angle. (ie: just jumping up and down on it does nothing, but if I push/pull from the front corner at an angle I can somtimes get it to squeak)

Maybe its just our dragons trying to get their wings spread. The funny thing is its the most annoying sound I've ever heard, I've gotten used to blasting the radio so I can't hear it.