Has he been to the vet in the last year? This could defiantly be a sign of infection and should be checked out by a vet especially if he develops any other signs of infection. Birds often do not diplay signs of illness as it is their natural instinct to act normal so they are not preyed upon in the wild.
On the other hand, if you are sure he does not have any illnesses going on you can try using a grooming spray. I suggest using a non-chemical spray such as this one.
You can also clean the cage and surrounding area w/ a water and vinegar solution (3 parts water 1 part vinegar) to help eliminate odors.
I hope this helps! Best of luck to you and your new friend!
Valarie Matthews -- Please click the "YES"/"ACCEPT" button to close the post if my information was helpful. Feedback & Bonuses are greatly appreciated!! You may reopen your question at anytime if needed.