engine tapping loudly

tapping sound from 1998 gmc jimmy...is it the lifters or bad oil pump...please help.:headshake

Lower intake manifold gaskets are a very common problem on the 4.3L engine. They can leak coolant into the crankcase which contaminates the oil. The early signs are: coolant level going down with no visible leaks and valve lifter clatter. Coolant in the oil will also ruin camshaft bearings, rod bearings, cylinder walls and crankshaft bearings. Have the cooling system pressure tested and repair all external leaks, (don't forget to check the heater core). After all external leaks are repaired, pressurize the system again and watch for a loss in pressure. If the pressure drops, chances are the lower intake gaskets are leaking.