2009 Edge SEL had developes a "growl" in the rear end. Sound is akin to the sound from aggressive tires, mudders and the like. If you were to hold a screwdriver aganst the tire treads and spin the tire faster and faster, that is what it sounds like. I replaced all four tires yesterday with new Michelins of the same size and model. Sound is still there. Not a harsh metal on metal sound and doesn't change when cornering. It does "speed" up and get louder the faster you drive. Starts being noticeble around 25 to 30 mph. At freeway speeds it is VERY noticeable. Vehicle has been a great one until this started a couple of months ago. Was very quiet, then they rotated the tires, and it was there. Hence the reason for thinking it was the tires. But now all the tires are new, high quality Michelins, and it is still there. Any ideas?