I've had both knees replaced. The left knee which had TKA 2 1/2 yrs ago is very loose & clunks like you described. The other knee which had TKA almost 2 yrs ago is not loose & doesn't clunk. The OS (2nd I saw) who replaced both knees said clunky or any other sounds don't matter as long as it doesn't hurt. That knee is so loose that when I was sitting on a low rolling stool & pushing myself along (painting baseboards) about 3 months after the TKA, the knee would start to dislocate - I could actually see the end of the bone bumped out to the side. When that would happen, I would quickly straighten my leg out so the bone would pop back into place. I told the OS & his PA about that & they told me that didn't happen. Hmm.. it happened quite abit but I was already unhappy with the OS so I just kind of dropped the subject.
Now, I'm seeing OS #3. He's very good with a lot of experience on more difficult cases. I went to him because both knees are still hurting a lot. During the first visit, he asked if my knees made any noises that could be heard by another person sitting near me. I demonstrated the clunking with my left knee. He said that was not normal & was indictive of a mechanical problem with the knee. I haven't pursued the problems with the left knee yet as the right knee is hurting the most right now. We're still trying to track down the problems with the right knee, & judging from my last appt last week, it looks like probably more surgery so it may be awhile before we start working on the left knee.
So I guess I can just say my left knee is the same as yours & my OS #3 says it is not normal & should be investigated further.