i have a 2000 model XR 200 and when it is idleing you can hear a slight ticking sound. i say slight ticking. but when the bike is in gear and being riden u cannot hear the noise. the ticking mine makes is quite normal.
any constant ticking (small ticking) on a 4stroke is the valves, adjust them and it should go away. now if it is a very loud ticking, ehh, ask some guys who know how to tear a bottom end apart, they could tell you what the noise is.