Noise coming from the knee is fairly common after TKR. Certainly check with your surgeon, but if it's minor and intermittent, likely it's nothing to be concerned about.

I have found that consistently working on my quads (squats, extensions, leg presses), and hamstrings keeps my knee capsule "tight" and so I don't hear any sounds. I think for most, though, some sound is common and not a cause for concern.