i recently had a 'click' i noticed it would only click when i applied pressure on the downward/forward part of my stroke. i did a search here and found out it could be a number of things.
loose chainring nut, loose crank arms, BB problems and one final one.
-> dirt/crap in my pedal to crank arm threading from riding in the raid a few days earlier. wiped em off, screwed em back in, problem fixed @_@.
suggestions for your problem. if you think its the chain, take it off. spin the cranks. still hear it?
if not checkin order pedals, crank arms, chainring bolts. if all else fails then have a look at your BB
edit: i type too slow