Oil light/knocking noise

I have a 98 Disco I and there is a knocking in the engine, not to mention when the vehicle stops the oil light comes on.  When the a/c is running the oil light comes on even with the vehicle moving.  We replaced the lifters and the oil pump but the knock is still there and the oil light is still on.  Any ideas?????  Thanks

This doesnt sound good 98. It sounds like an internal problem , lifters,rings or valves. I assume it has enough oil in it?  What color smoke comes out of the exhaust at startup? Does the lr jump around while the knocking is going on? Check Ignition first ( plugs , wires, distributor or coil).See if the plugs are wet.( water is a bad sign) Oil is not so good either,A little fuel is ok , but not sopping wet
Maybe you'll get lucky and it wont be anything major.Was it doing this before you put the oil pump on? 

Have you done a mechanical oil pressure test to verify what the oil pressure is at idle and at 2000RPM's both when cool and at operating temp. Have you pulled the oil pan, checked any of the main bearings and the oil pick up tubbe?
Mike

Sounds like the main bearings are worn out.

it was my oil pick up tube, mechanic cleaned it out, worked fine!
 
Ralph

The noise was there before replacing the lifters and oil pump.  I'm afraid to ask what the cost would be to replace the main bearings?????