I had the same situation--clicking sound post op.
Physical therapist informed me that I should
not be concerned unless there was associated pain.
Well, I had no associated pain and the clicking
sound is no longer present.  

Could it be a piece of meniscus?  Yes.  
Apparently, there are many other reasons, too.
Most are not a big deal.

It lasted for about 2 weeks.  I did not have this
sound pre-op so I was quite concerned when
I first noticed it. By the way, the clicking sound
that I had was associated with riding the
stationary bike in rehab.  The PT actually
stopped me from doing the bike for a while.

Remember that I had absolutely no associated
pain with this clicking sound.  

thank you so much. my PT got me freaked out and didnt offer those reassurances!  i could feel the click too.. and it is loud- yours too?

After all of my surgeries my knees ahve mad weird noises like never before.

Some of it was due to scar tissue and probably also swelling and impaired ROM.

I paniced after my recnent op that my knee was clicking as I thought the op was a failure but when i rang the OS he said he would be more worried if it wasn't making strange noises!.

Unless there is any pain or unusual swelling, please don't worry, look on it as a party trick!

Iona