Rear of vehicle is squeaky, help!

My 2007 Honda Element is very squeaky. It appears that the noise is coming from the rear wheels of the vehicle and happens when the car is turning and sometimes just driving down the road. I have taken it to my mechanic, and they looked it over. They said there is nothing wrong with it besides it needing to be lubed up. They said my brakes, bushings, etc. are all fine. They lubed it up and it is only slightly better. They told me that I will have to get them to do it every few months until it is saturated. They did not charge me for anything, which is good. There has to be something that none of us are seeing. Please help!