Oil pressure

You could try a thicker oil (say 20W50). If that doesn't help you could have a bad oil pump or worn main bearings. How many miles on the engine?

You could also try adding STP oil treatment to thicken it up.

There can be a few causes such as low oil level,injectors etc some cars are worse than others my Subaru outback you could literally hear the injectors but in your case I'm leaning towards your valves are out of adjustment which can happen after normal wear and tear.. if you pulled your oil pan then your obviously more than capable of checking your oil so I doubt your oil was so low it was causing the noise your hearing so again I'm definitely leaning towards valves out of adjustment. Which if you feel confident enough it isn't hard to check the adjustment just need a feelers gauge and would definitely be helpful to have a Haynes manual for your car so you can get the gap specs for your valves but a quick Google search will give you in depth guide to check your valves..

Boostdy8 I skipped the valve job all I did was spray painted the head where meets the block and filed off until there was no paint list with a fine file I never did nothing with the valves other than taking off the rocker arms and pushrods cuz I have anything to do with the valves plus my oil pressure light coming on inside the car when this starts happening