Some air tracks produce an ultrasound tone from the air holes which interferes with the transducer. Adjust the air flow so that the cart just barely lifts off of the track. If you still have interference, slowly increase the air flow until the interference stops. Finally, if you still have problems build a "megaphone" for the front of the Sonic Ranger by cutting the bottom out of a Styrofoam cup and taping this to the front of the transducer. Then tilt the transducer up slightly so that it can't "see" the track but can still see the gliders.
Diagram 1: Megaphone and Sonic Ranger Setup