Is cracking during yoga healthy?

I've began dedicating at least an hour of intense workout a day, along with an hour and a half of yoga, for about three weeks now. I've noticed I seem to excessively crack in my knees during, and sometimes after if I kneel. I know it's not unusual to crack during yoga, although no other part of my body is actually cracking.

I've had physical therapy for my knees in the past (about 5th grade) because my cartilage was uneven. I also needed strength training for my outer thighs because my knee caps had the tendency to slide to the inside of my legs. I know this might have something to do with it, but I haven't had problems with my knees for about 5 years now. They occasionally crack, but I have no pain. I have no pain during yoga either.

Should I be concerned that they crack? I know repeated cracking can be damaging, and I don't want to over do anything and bring back any problems I previously had. I've read around a little bit, but nothing directly answers this question. Thanks.