You probably want to find out exactly where its coming from. Someone in one of my threads suggested that you get a card board tube maybe one from a papertowel roll and put it up to your ear and pinpoint where the sound is coming from.
Didn't use this method but I had the same problem. Not sure if it was before or after I OCed but I noticed it within the last few weeks. Didnt bother me until now and it turned out to be a case fan. I replaced the case fan and no more annoying clicking noises.