Croaky Crowing :-(

One of my boys crow has gone very croaky in last couple of days. He sounds like his batteries are running down lol poor soul. 

He has no other symptoms. His eyes are clear, no sneezing or wheezing.... just croaky crowing. He is eating and drinking and looks just as normal too.

Do I need to seek advice or shall I give it a few days and see if it clears? I have tonic (pink gin i call it lol) in his water and also plain water for him too.

Thanks x