I have had a whistling sound when exhaling for a year now. no cough or other symptoms. nasal scope and ct scan found nothing. what else could this be?

?septal perforation?: Whistling/wheezing noises happen when airflow is partially obstructed and a turbulent gradient is created. This can be temporary, as in asthma with a closing of small airways, or the result of injury to part of the upper respiratory tract (as in the perforation of the nasal septum that happens with cocaine use). A careful ENT exam should reveal.