Cars have so many different parts working together that you’re bound to hear a few sounds while starting and moving. Although some sounds are natural and have no cause for concern, you should become suspicious if you hear loud rattles or knocking sounds under the car when accelerating.
Car owners must also be careful about the location of the noise and look immediately for the fault. If you also hear knocking sounds under the car when accelerating, there is a probability of one of many parts malfunctioning, including the engine, suspension, and transmission.
A knocking sound is like a slap or hard impact noise that is essentially generated by two metallic or hard surfaces touching. Let’s take a look at some of the most common causes of strange and knocking sounds from the underbody area and understand how you can fix them.
Here’s why you hear a knocking sound under the car when accelerating
There are a few reasons you hear strange rattling and knocking sounds from under the car when accelerating. These are some of the most common;
Problematic Water Pump
One of the most important and active parts of a car engine, the water pump regulates the flow of coolant through the radiator. If the water pump is damaged or has loose parts, you’d hear a knocking sound when accelerating as it is located near the lower part of the engine bay.
Failing Catalytic Converter
A catalytic converter is a crucial part of most modern cars and reduces harmful emissions. It has a honeycomb structure inside which gets clogged over time.
If it is not serviced or replaced timely, the internal parts can bounce and rattle inside the metallic container, producing a knocking sound. It is also located on the lower part of the engine bay, so the sound comes from under the car when you accelerate.
Poor Quality Fuel
If you have filled up your gas tank with leaded fuel or something with lower RON, it is going to create problems. When the fuel with lower RON burns, it leads to a poor/incomplete combustion process and a premature blast occurs inside the engine.
If you hear a knocking sound under the car when accelerating, it is highly likely that the poor quality fuel is the culprit.
Spark Plug Issues
Spark plugs initiate the combustion process by igniting the air-fuel mixture in the engine. If the spark plugs have become rusted, damaged, or not replaced on regular schedules, the combustion process would be affected.
Incomplete combustion or strokes would lead to knocking inside the engine and become more frequent if all of the spark plugs have gone bad.
Timing Chain Problems
If the timing chain becomes loose or damaged over time, it produces crackling or knocking sounds when the accelerator is pressed and goes away on releasing the pedal.
Timing chains should be adjusted and recalibrated every 50,000 miles, otherwise knocking sound is most likely to appear whenever the car is accelerated.
Bad CV Joint
If you hear a knocking sound on acceleration when taking a turn or rotating the steering wheel, you should immediately suspect a bad or worn-out CV joint.
A CV joint is an important part of a car that gets worn due to bumps and maneuvering on rough terrains.
Worn Axles
If you hear a knocking sound under the car when accelerating and nothing is wrong with any of the engine parts, it could most possibly be worn axles.
Due to rough roads and uneven surfaces in most regions, the bearings of the axles get damaged over time and generate knocking sounds upon acceleration. Replacing the axles and CV joints is the only way out of such trouble.
Damaged Suspension
A car’s suspension bears all the grunt of the road and hazards of the terrain, yet does not give up so easily. Suspension of a car also has some weak areas and points, such as bushings and rubber seals, that can get damaged or leak easily if the car is not looked after properly.
If you hear knocking sounds coming from under your car when accelerating, a damaged suspension must be acting up.
Failing Ball Joints
Ball joints are one of the most easily wearing parts of a car and if not replaced timely, can create rattling and knocking sounds that increase in intensity upon acceleration.
If you also hear knocking sounds from under your car when accelerating, you should suspect faulty ball joints, particularly if your commute involves driving on rough patches and bouncy roads.
How to Get Rid of Engine Knocking?
It is crucial that you get your car checked and fixed by a professional to get rid of engine knocking and resolve the problem durably.
1. Start by looking at different parts and locating the issue, such as bad spark plugs, water pump, engine mounts, or the timing chain.
2. Try refueling from a different station and use premium fuel. If the problem goes away, it was most probably the poor quality fuel.
3. Also get the spark plugs, water pump, catalytic converter, and throttle body examined, and replaced immediately if found to be at fault.
4. Try to get the ignition process in line by getting the ECU reflashed, the intake and exhaust manifold serviced, camshaft and other important parts checked.
5. Replacing weak engine mounts in high-mileage cars is one of the definite solutions to engine knocking, if nothing else is working.
Final Thought
Cars are machines that are bound to produce some sounds and should be considered natural. But once you start hearing knocking or strange noises from any part of your car, it should raise some alarms and you must get it checked immediately. The most common source of knocking sounds is the engine, so once you hear a rattle or knocking sound under the car when accelerating, it’s time for a trip to the workshop.
