knocking

slower knocking not rapid tapping/ticking would indicate a bearing clearance on the crankshaft is out of spec or not getting enough oil. what weight of oil are you using and is it clean? how loud is the knocking? when did it start? if it's not really loud and sharp you might try a heavier oil or an additive like lucas oil stabilizer.

Check the oil pressure with a mechanical gauge,could mean oil pump and engine bearings

It's rapid. Kind of sounds like the sound a card makes when put between the spokes of a bike tire. Mostly hear it on acceleration. I am using 10 40 oil. I added a quart of oil and drove it down the road a bit. The sound improved some, but then the oil light came on again. When I got back home there was oil on the engine, which hadn't happened prior to adding the oil.

Also, sound is at the top of the motor and the oil appears to be coming from the valve cover.

when does the oil light come on? at idle or while engine rpms are higher than idle like when you are driving,not stopped. when did this problem start? if the noise is louder on acceleration that point to crank/rod/piston knock.what does your oil level say? how bad is the leak?