The clicking is not any loose part or anything to worry about, when you click it sometimes the part that connects the button to the macbook just retracts wrong.
I am experiencing the SAME exact problem! It just started making the noise today, and I purchased by Macbook Pro in December. Did you take it the GeekSquad? I'm worried because I had a PC before this, and even though it's not a functionality issue, I am worried that it's a sign of deterioration. What did you do?