I have a 2007 ford escape with 12000 miles on it. A month ago it started making this loud noise in the AM...only when cold. It happens when I get in the car and the air is on, but on 1...not revved. When I put it in reverse to back out of the drive or garage it makes this loud engine noise. If I turn the air off. It stops. WHAT IS THIS? dealer is not helping. Friends and family hear it so I know I'm not nuts. HELP