Low rpm rattling noise?

my 2010 legacy is making a rattling/vibrating noise that i can hear at 1.5 rpm between 10-40mph. it sounds like its coming from the front left wheel area. the dealership thought it was the heat shield... wasn't... then they thought that might be the bearing... wasn't. they told me maybe it was my tires... it isn't. anyone have any idea??? done some research and i think could be something with the cv joint or maybe a cat. any ideas