Blackbird with no voice?

We have a young blackbird who can just about fly and can feed itself but when it tries to call it sounds like a cough/sneeze...or his beak opens/shuts nothing comes out! Never experienced anything like it. It seems ok in all other ways seems to like company and waits for us to go out in garden or will suddenly appear if we are out there..very tame comes up to our feet and we are walking round it if it dont want to move! Just concerned why it cant squawk or call out.