Engine clicking noise

What's the question? Has the oil pressure been tested with a mechanical gauge? If it is low you need to find out why before serious damage occurs if it hasn't already.

You already know. The warning light means the oil pressure is low. The hydraulic lifters in the engine fill up with pressurized oil to take up the slack in the valve train components which makes them quiet. With no or low oil pressure, those lifters don't pump up and you can hear the valves clatter. That noise in the upper engine is not serious in itself but it's an indicator that other engine parts are being damaged. The low oil pressure means the engine bearings aren't getting sufficient oil and the pistons are scuffing the extremely smooth cylinder walls.

An engine without oil pressure can run almost as long as a human body without blood. Low pressure can be caused by something as minor as low oil level so the pump sucks up air instead of oil, or it can be caused by worn engine bearings that let the pressurized oil run out too quickly. Regardless of the cause, low pressure prevents the oil from getting to many places that need it to isolate moving metal parts from each other. Your mechanic must determine if something is preventing the oil pump from developing the needed pressure or if something is bleeding the pressure off faster than it can be built up.