Why does a rattling noise come from Mercedes Benz when accelerating?

This blog will answer the following questions: Why does a rattling noise come from Mercedes Benz when accelerating? How to diagnose a rattling noise coming from a Mercedes Benz? 

Why does a rattling noise come from Mercedes Benz when accelerating?

A rattling noise can come from Mercedes Benz when accelerating due to the following reasons:

• Noise from the engine mount
• Noise from the exhaust system
• Noise from the suspension system
• Noise from drivetrain 
• Noise from the Brake system

Let’s take an in-depth look at each of the causes of a rattling noise in Mercedes Benz cars:

Noise from the engine mount

The internal combustion engine in Mercedes Benz cars is mounted on a subframe or front axle carrier. The engine mount absorbs the vibrations from the engine and prevents them from reaching the chassis.

The engine mounts are covered with a heat shield in order to prolong the life of the mount and protect it from the heat of the combustion engine. As the engine mount gets loose, the heat shield connected to the engine mount starts to make a rattling noise.

The noise is present only when accelerating because as the engine speed increases the vibrations that reach the engine mount from the engine supports also increase. The remedy is to perform a visual inspection of the engine mount. If the threads inside the mount are damaged then they must be replaced. It is not possible to re-torque the engine mount bolt on a damaged thread.

This problem is more common in Mercedes-Benz cars that are powered by gasoline engines. The gasoline engines operate at higher engine speeds for a longer duration compared to diesel engines.

Noise From the exhaust system

The exhaust systems in Mercedes Benz cars consist of the catalytic converter and various sensors to monitor the emissions. The exhaust system is connected to the exhaust manifold by sealing rings and metal brackets.

There are also rubber mounts with hooks to hold the exhaust system in place. If the rubber mounts are worn out then rattling noise can come when accelerating. Also, noise can occur if one of the exhaust clamps is loose. 

The sound of the exhaust system also changes as the exhaust gasses are leaking from loose clamps. Improper fitment of the exhaust system during production or if it was removed is responsible for the rattling noise. 

In the Mercedes Benz cars with higher age and mileage, Rust and corrosion in the exhaust system can also be one of the causes of rattling noise.

Noise from the suspension system

Mercedes Benz cars use an independent suspension system in the front and a multi-link suspension system in the rear. There are upper and lower control arms with ball joints and bushes in the front.

If the bushes in the suspension system are worn-out then as the vehicle accelerates, a rattling noise starts to come from the underbody of the vehicle.

A visual inspection of the suspension components is required to identify the source of the noise. Mercedes Benz cars also have underbody metal shields in order to protect the fuel lines and engine oil sump. If the metal shield is also loose, it can rattle as the vehicle is accelerating.

Noise from drivetrain

Mercedes Benz cars have complex drivetrain components, although the noise complaints from the drivetrain are rare, they can occur regardless of age and mileage of the vehicle. One of the common causes of rattling noise is an excessive play between the crankshaft journal bearing.

The noise increases with an increase in the engine speed and can be difficult to diagnose, the damaged bearing is renewed and a complete engine rebuild is required to fix the problem. Similarly, a damaged flex plate can also rattle between the timing case and the torque converter housing.

Other cases of rattling noise from the drivetrain are misaligned propeller shafts, faulty camshaft adjusters, and an elongated timing chain. Rattling noise when accelerating from the drivetrain components is very expensive to fix as it requires major disassembly.

Noise from brake system

Mercedes Benz cars have disc brakes on all four wheels, latest cars use electronic parking brakes. However, older models used drum brakes on the rear axle as a parking brake. The drum brake assembly starts to rattle if the pads are worn out.

The rattling noise only starts when accelerating as the parking drum brake is not applied. In some cases, the entire parking brake assembly can need replacement if the vehicle is driven without replacing the brake pads.

Some of the other causes of rattling noise from the brake system are loose or bent back plates, excessive runout of the brake disc, and loose caliper pins. Most of the models use a floating caliper on the rear axle and if the brake pads are worn out, the pins can rattle as the vehicle is accelerated.

How to diagnose a rattling noise from a Mercedes Benz?

The procedure to diagnose rattling noise from Mercedes Benz is given below, always consult an authorized workshop to rectify abnormal noise problems.

• Perform a test drive and note down the speed at which the rattling occurs. Also, observe the area of the noise. For example, the front or rear side and top or bottom.
• Once the location is identified, perform a visual inspection of the area. Look for loose parts or worn-out suspension components that can cause noise.
• Lift the vehicle on a lift and check if all the screws of the underbody shield are tight. There should be no debris on the underbody shield as it can also cause rattling.
• If it is hard to locate the source of the rattling, eliminate any other noises present in the car and try to recreate the noise by replicating the condition under which it occurs.
• Re-torque bolts of link rod, and stabilizer bars and perform a road test again to check if the noise is rectified.

Mercedes Benz authorized dealerships also have special tools that can be used to diagnose the rattling noise when accelerating. Some of the special tools used are noise detectors that contain a series of microphones.

The microphones are attached to the vehicle and the driver can listen to the noise in the headphones. It is really helpful to use noise detectors as it eliminates repeat repair jobs.

Another special tool is the Xentry NVH vibration analysis tool which comes with a strong microphone that can record noise as well as vibration as it occurs. The data can also be transferred to a USB for warranty claim purposes.

Conclusion

This blog explained the causes of rattling noises found in the Mercedes Benz cars. Most of the rattling noise complaints are easily rectified and do not require expensive repairs. Therefore, it is important to get the vehicle checked if any rattling noise is present when accelerating.