Are you hearing a tapping, pinging or knocking sound coming from under the hood of your car? No, your engine isn't trying to communicate to you in Morse code -- but the sound it makes is telling you that something is wrong. We'll help you narrow it down on this page. There's a very specific condition called "engine knock" that can create such a sound, but there are many other problems that can cause what a lay-person might describe as a knocking noise. We'll detail four of them for you below.

noise from car

If you detect a rapid pinging, tapping sound coming from the engine as you drive, your engine could be suffering from a knock. You may find this problem gets worse as you accelerate. Engine knock is what happens when a portion of the fuel inside the cylinder detonates before the rest of the fuel. When your engine is running properly, the spark plug begins the process of combustion, burning up all the fuel inside the cylinder in one, controlled explosion. If the octane rating of the fuel you've used is too low, or there's another damage elsewhere in the engine, some of this fuel may detonate prematurely. These detonations create the knocking or pinging sound.

Make sure you're using premium fuel in your car if your engine requires it, as using regular fuel in a car designed for premium fuel is a recipe for engine knock. Engine knock can also be caused by incorrect ignition timing, an incorrect air/fuel ratio, or a malfunctioning knock sensor.

While engine knock is a well-known phenomenon among auto mechanics, there are plenty more things that can cause what you might describe as a knocking sound. For example, as the engine turns, it drives a belt that rotates pulleys on all sorts of accessories under the hood to give them power. These accessories include the water pump, A/C compressor, power steering pump, and possibly more. If these pulleys become cracked, bent, warped, or otherwise damaged, they may begin to rattle as they rotate. The faster the engine spins, the faster these pulleys rotate, which could cause the noise to become louder as you accelerate.

If it's not the pulleys, it could even be the accessory belt itself causing the noise. If you'd describe the noise as a loud, high-pitched, squealing, squeaking or chirping noise, you might have a bad belt. A belt that is slipping stretched out or glazed with something like engine oil might start to make noise, particularly when the engine is cold.

The last possible cause of a knocking noise from your engine is called rod knock. This is the loud clacking noise you may hear if the piston rod bearings become damaged or misaligned. Deep inside the engine, the pistons are attached to the crankshaft. The piston rod encircles the crankshaft with bearings so that the crankshaft can spin and the piston can travel up and down smoothly. Damage to these bearings can allow the rod to knock against the crankshaft, due to a small gap created between the piston rod and the crankshaft.

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