Hello, I drive a 2015 Scion tc. When I have the heat/ac on, a weird noise almost like a metallic noise can be heard when the engine is under load. Would anyone have any idea what would be causing this? My local dealership has checked it out numerous times and claim they cant hear it or cant find anywhere that may make this noise. It sounds like it may be something rattling but when I begin rolling you can hear it start for a few seconds then stop. The noise is coming from the front of the car. Thanks.