Fast Breathing Noise from Nose. Reason?

My son had this weird thing happen last time where he has this fast Breathing sound coming from his nose during Aug-Sep. We have shown him to the chest specialist also. We have got X-Ray, Chest CECT, Laryngoscopy, Bronchoscopy done and every report came normal. And suddenly after two months that noise went away. Now again from today he has a little cold and rubbing his nose. And again we are hearing that fast Breathing and deep breathing sound multiple times. He is playing well and eating well. Can someone tell what this is and why this is happening? We have shown him to pediatrics today and there is no congestion. The doctor has prescribed Otrivin P and Alex Junior. These sounds are making me and my wife mad. We don't know why this keeps coming back and what's the reason?