Help da*200 maybe faulty

This is my second copy of this lens. The lens hesitates to lock focus. The centre point flickers and I can here the elements clicking and when it does the image quality is inconsistent sometime sharp sometimes soft. Is this usual.

What camera are you using it on and what settings, how dark is it? All these things have to be taken into account. Try a well lit environment, make sure the lens is wide open f2.8 in this case and also try it with live view to see if there is a difference.