Check both the bolts that hold the lower control arm to the frame of the car. My car was doing the same thing, we replaced the coil spring perch thinking it was that. We finally found that one of the bolts for the control arm wasn't tight, just simply tightening it up fixed the problem. It was making a squeaking noise going over a bump or when you hit the brakes hard. Very similar to the sound of a bad lower ball joint.