Thanks for writing in.
With a history of total knee replacement
two years ago, I hope you continue regular visits to your doctor.
Right now I would suggest you to consult your doctor and allow your knee to be examined and alert him about your exact problem.
A X ray
might be needed to see if there is any loosening in the artificial knee joint and that might be causing the cracking noise. It might be in initial stages and hence you are not experiencing any pain or swelling.
Hope this helps.