2002 Jeep Liberty tapping sound in engine

Yesterday my jeep started making a tapping sound. It is a faint tap and not a loud knock. I am concerned that there may be something seriously wrong with it. I checked the oil level this morning and the level is ok. I really cannot afford a repair this time and wondering if maybe an additive may help? Any suggestions would be helpful. The tapping sound seems to be coming in the area of the engine by the oil fill area.