Sound while breathing. What can i do?

Hi doctor...My baby is 10 months old.He is 8 kg.since birth he has been making sound while breathing occasionally.There is no visible cold,cough,mucus in nose and nothing but  makes gur gur sound.I tried cold over syrup and mucolite several times based on our doctor's advise. His chest was clear then as per the x-ray.since 15 days he has been having sound again.I took him for vaccination on 6 th of thjs month.Doctor checked him and said everything is normal.He is making more sound from 3 days and i could listen some sound when i kept my hands over his chest and back.I tried nasal saline drops but of no use.He is breastfed and having some fruits and cerelac.what could be the reason for making such sounds??Is there anything to worry??what can i do??