A failing oil pump will create a whining or whirling noise. Failing oil pumps will also have several other loud noise that will accompany it, such as a overly loud valve-train and bottom-end assembly.
The whirling noise developed by a failing pump is due to the internal gear mechanism wearing down. When the pump fails completely, the rest of the engine will face oil starvation, which will lead to a very loud engine.
When the valve lifters are not properly lubricated, the valve-train will hit against each other creating a clacking noise. The connecting-rod bearings will also dryly rub against the crankshaft, which will cause a knocking noise. All these problems can only be repaired through a complete engine overhaul.