Its good to find somebody else at this stage, I'm nearly 11 weeks post op (Patellor Tendon Graft). I'm not sure what the popping could be, I had something similar to what you are describing when I ruptured my ACL and was going through a physio regime to gain some fitness before the reconstruction, it eventually disappeared, one of the physio's mentioned something about a tendon. I must admit to being very self conscious at the moment and notice every crack or groan that my body makes, I'm feeling old even though I'm only 26.
I've just started working out on the exercise bike (2 weeks) and stepper machine (2 weeks), but am still trying to cautious, maybe over cautious at times.
Anyway keep up the good work, enjoy your break and good luck with the rest of your rehab