I have whistling when exhaling. doctor said lungs sound clear and the whistling is heard over the neck. x rays, laryngoscopy, pft all normal. causes?

Throat tightening: First one needs to find out if you are tightening up your throat when you are breathing out and thus the whistle. When this happens next time, relax your lower jaw to see if the whistling disappears. Although the PFT was normal, was it obtained at the time you had the whistling? If not, then asthma must be considered as well given that asthma is often an intermittent disorder.