My 2008 RX 350 has a squeaking, screeching metallic noise from underneath the car. I have taken it to the dealer 4 times. St first I was told the muffler assembly was loose and tightened up, then the muffler gaskets were worn and replaced 2 times. The noise is still there when I park on level or an incline. Is this a defective suspension or what?? My award winning dealer has not fixed it yet. What should I do?