I get off the bus today after school. It's about -10F. I hear a plane coming overhead departing MHT. It appears to be a USAirways Airbus. It sounds normal....as it gets closer I hear a LOUD sharp whistling noise from the engine. Just like a LOUD Nerf Football! As it passes over and leaves me behind the noise starts to disapear and I no longer hear it. The planes are normally about 9-10,000FT when they pass overheard. Any ideas on what that noise was? I was curious as it sounded VERY unusual and not like a normal airplane engine. My only guess was, cold air? Which makes NO sense.