I just had surgery on my left knee for a torn meniscus, however my right knee is also popping?

Tell your doc. Your orthopedic surgeon will exmaine it and decide if you need imaging or arthroscopy.
Not unusual. This can happen. It can represent several things...Joint fluid movement, tendons rubbing over the bone, cartilage wear, and it may have even been there before but was not as noticeable. Continue the pt rehab, and it shouldn't be painful while it pops. If it is painful, you should consult your surgeon. It is also possible you may have retorn a meniscus.