Wheezing?

[BudgieWorld]

Hey all! I have a parakeet named Cotton that I have had for about 2 years. He started behaving aggressively so I worked with him a little bit more than usual. I was having him out when one day I noticed that he was wheezing when he was breathing. It is not constant, though. Sometimes he is fine. He doesn't show signs of sickness: eyes bright, vent clear, no discharge anywhere, no missing feathers, and he is still preening, chirping, and eating. So I am not sure what is going on with him! Right now he is preening and chirping happily, although he is not coming out of his cage, although I have his door open, but this isn't unusual.
thanks for your time and I hope that he will be fine!!