An engine knocking could mean several different things and it could be as simple as the fuel and air mixture not being correct causing the engine to explode the fuel incorrectly which can cause the engine to knock.
Then it could be a rod knocking which requires disassembly of the engine to repair the engine main bearing and rod bearings.
If your engine is knocking you need to get it checked soon before it destroys the engine and requires a more expensive repair.
If the engine is making a ticking like noise then it could be the lifters causing the problem.
But either way you need to get the engine checked because an engine should not be making a knocking sound because if it is then something is seriously wrong and you could even blow a rod through the engine or engine oil pan.