1 and half years old female budgie has respiratory problems (significant and loud cracking- and wheezing-sounds during each breath) for half a year. She’s otherwise healthy.

What may be the cause? Is it asthma, chronic inflammation of lower respiratory tract or maybe some mites? May there be some obstruction in the airways, either foreign body or even tumour?

Please advice me of possible causes and appropriate treatments of them. Thank you very much!