Your Valve Lash Requires Adjustment
Valve lash is the distance between your valve stem and, in your case, the rocker arm. You have a camshaft inside your engine case or 'bottom end'. The reciprocating actuation is transferred to the top end via a push rod which contacts the rocker arm which actuates your valves.
Increased valve lash over time is a normal event and is a part of normal maintenance of your vehicle. Over time, as your engine wears in, and valve lash increases. The sound is a repetitive ticking noise that matches the RPMs of your engine. It can be a bit loud and annoying but it isn't a critical event. You do need to get it adjusted or do it yourself though, if not, it will continue to wear and possibly damage your engine.
Valve lash can be adjusted by removing the rocker box cover to reveal a threaded shaft and a lock not adjust shaft length.
Here is some additional informationHere is some additional information regarding your valve tick.