If your vehicle is showing loud metallic knocking or clanking noise from the engine, here are the most likely causes and the parts you'll need to fix each one.
Low oil levels or degraded oil can cause hydraulic valve lifters to lose pressure and fail to pump up. This results in a loud, rapid metallic clacking or tapping noise from the top of the engine.
A worn serpentine belt tensioner or a failing bearing in the water pump or alternator can create a loud, erratic metallic clanking. Because it is bolted to the engine block, the noise often sounds like internal engine damage.
A completely failed engine mount allows the engine to physically shift and hit the metal chassis or subframe. This causes a loud clanking or thumping noise, especially when shifting gears or accelerating.
A cracked flexplate or loose bolts connecting it to the torque converter will produce a loud, rhythmic knocking noise at the back of the engine. This is frequently misdiagnosed as severe internal engine failure and often occurs after recent transmission work.
If a spark plug is not torqued properly during installation, it can back out. The escaping cylinder compression creates a loud, rhythmic popping or knocking sound that matches engine RPM.
Severe internal wear to the connecting rod bearings creates a deep, heavy metallic knocking sound that gets louder and faster with engine RPM. This is a catastrophic failure usually caused by oil starvation or extreme mileage.