If your airways are narrowed for some reason, you may hear a whistling or whining sound when you exhale, says Dr. Pennell. The symptom can be caused by problems such as asthma, emphysema, as well as lung cancer (wheezing may result from air pushing past a tumor that’s pressing on the airway). “This sound concerns people because you usually don’t hear yourself when you breathe,” he says. On the other hand, a lot of long-time smokers are so used to wheezing that it stops setting off alarm bells. Remember: Wheezing isn’t normal, so get it checked out.