could just be a little overflow from the coolant resevoir dripping on the exhaust. when it runs hotter (like when your running it hard) you may get a little overflow in the cooling system. the resevoir is vented, so if it gets real hot, and the resevoir fills up, some coolant will come out of the vent. check the coolant level when the bike is cold, if it's over the "cold" line, it may just be over full.