Pull the coil packs one at a time while the engine is running if the knock gos away at #3 you have a bad rod bearing on #3 or the 2 crank bearings adjacent to that rod. Do a cylinder leak down test if you hear air pumping into your intake you have a bent intake valve. If you hear air in the exhaust you have a bent exhaust valve. Do a compression test if it is low squirt some oil in the cylinder if it gos up you have bad rings. Take your oil pan off take a peek see if the rod is sow bent it is rubbing the cylinder also look at your cylinders for 4 corner seizure this causes the piston to slap.

http://www.pwab.org/PISTONDIAGNOSTICGUIDE.htm