Your car is idle on the road, waiting for the green light to move forward. A disruptive, rattling noise arises from the heart of the engine just at that moment. Annoying, no?
So why do you hear a rattling sound in the engine at idle? The rattle noise in the engine occurs due to low engine oil pressure and any loose parts or panels inside the engine, such as the exhaust system heat shield. Moreover, a damaged catalytic converter and spark plug can also be the culprit.
But this rattle or knocking sound can get even more complicated than you think if untreated. In this guide, I will focus on and explore the root of this issue extensively. So, without further ado, let’s take the tour, shall we?
Why Does Engine Make a Rattling Sound at Idle & How to Fix?
In terms of engine rattling noise, knowing the ins and outs of the situation effectively makes it easy to solve. So, let’s focus on why such sound surfaces and how to fix it.
1. Low Engine Oil Pressure
When your car or other similar vehicle is idle, engine RPM (Revolution Per Minute) drops to the lowest. So, the pump does not distribute oil effectively as it does at higher RPM due to low oil pressure.
As a result, critical engine components such as wheel bearings, camshaft, driveshaft, and valve trains are not lubricated enough. The result? Well, an enhanced friction between metals results in a rattling noise.
Besides, low oil pressure causes clearance issues inside the engine. So, when the components heat up and expand because of the friction, starvation of oil creates a rattling sound when the metal parts come in contact.
Oil pressure can happen due to reasons like:
- Low oil levels,
- Faulty oil pumps,
- Oil hose leaks, and other failing components.
Fix
First of all, remember that continued low oil pressure in the engine can cause permanent damage, and it will be way costlier to repair it. Not to mention the normal valve train or fuel injector clicking.
Here’s how you should approach to fix the issue:
- Perform and oil pressure test. For most users, I recommend going to a repair shop to get help from a professional for this. They will measure and check whether oil pressure is ok.
- Check for the faulty pump. See any physical wear and tear. Check if the oil pump makes an unusual noise. If so, replace the oil pump.
- Inspect oil in the fuel tank. If they seem to be on the lower than usual, refill it.
Also, you can use an oil additive, which will improve oil viscosity and reduce friction.
2. Loose Engine Heat Shield
A loose heat shield can be another leading reason why you encounter clattering, tiny metal noise. At idle, the engine generates moderate vibration. If the heat shield is loose, it will vibrate against components in close proximity.
Now, as the heat shield is located somewhere around the exhaust components, extreme heat often expands the shield plate after a good while. Consequently, its position may shift ever so slightly, and that produces the rattle.
You see, this annoying sound is more pronounced at idle because it masks the minimal exhaust sound in this circumstance.
Fix
Fixing a loose heat shield is a straightforward task. Just tighten the fasteners and brackets holding the plate in place. If that does not help, take it out completely and then reattach it correctly.
That said, screws and bolts sometimes wear out after a while. So they can not hold the shield firmly, and it wobbles. Simply replace them with new ones.
3. Broken or Loose Catalytic Converter
The catalytic converter, the very exhaust emission control device, is a potential perpetrator that can produce a rattling sound at idle.
See, the catalytic converter basically transforms toxic gasses into less hazardous exhaust gas utilizing a redox reaction. If this unit is damaged, it will create annoying sounds during the process. But this can generate the impression that the engine is making the noise.
A ceramic honeycomb structure and some catalyst substrates inside the component may break apart over time. And it eventually generates a rattle-ticking noise.
Fix
A broken catalytic converter requires a replacement. Look out for any signs of corrosion, rotten eggs smell from the exhaust, black smoke and unusual heat exerting under the vehicle. A replacement part will cost between $70-$130. Inspect the entire exhaust system to ensure that the catalytic converter is securely mounted and that there is no missing clip.
4. Tappet Noise
There is a distinct clicking sound in older engines with flat tappets. This is known as the lifter noise. In these engines, you’ll see holes. Tappets or lifters are located in these holes.
When the camshaft rotates, the engine’s hydraulic valve lifters move up and down. Oval lobes of the camshaft force it to move up, and valve spring pressure pulls it down.
In the process, the lifters travel inside the camshaft lobes. As the assembly ages, tappets get dirty and stick in the hole. So, as soon as the camshaft hits the bottom, it creates noise, which you identify as rattling.
Fix
First of all, inspect the lifters when the noise occurs. To do that,
- Remove the valve cover. Or you may need to remove the intake manifold cover on some vehicles to access the lifters.
- Check whether the tappets are worn out, damaged, or dirty. Replace them with new lifters.
Now, use the correct grade oil and filter to clear out the oil passage and restore the tappet compression. Use cleaning additives to remove dirt and debris.
5. Bad Spark Plug
The spark plug creates the ignition to start the engine. It also ignites the air-fuel mixture frequently when you accelerate your car from idling. But if it is in poor condition, the timing of the spark becomes inconsistent, and as a result, premature ignition takes place.
Irregular firing from the spark plug causes rough engine operation. Hence, a rattling or knocking sound is heard from the engine.
Fix
In terms of spark plug issues, it is best to replace it with a new one. If the problem is not addressed correctly, it can cause major engine failure down the road.
6. Incorrect Piston Movement
The piston within the cylinder in the engine can sometimes hit the wall; this incident is known as Piston Slap.
Leaving enough clearance for thermal expansion and lubrication, the piston is placed inside the cylinder. But it is designed efficiently so that the piston does not wiggle much.
That said, after years, it can wear out and move more than it should inside the cylinder. That is what lets the piston hit the cylinder wall. So, the noise emerges.
Not to mention, worn piston rings also let the piston move more freely than it should.
Fix
Piston slap is the most notorious source of engine noise at idle. And it really does not have a rapid DIY fix, to begin with. It requires disassembling the engine. So, seek help from a professional car engine mechanic to get to the bottom of this issue. This is one of the most costly repairs to the engine. It can go up to $4,000, including labor charges and parts.
Rattling Noise in Diesel Engine at Idle
While diesel and gasoline engines generate power with combustion, both go through a completely different approach to achieve that. This is a reason why they produce unique noises in their own ways.
Touching on the clatter of the diesel engine, the injectors can create a lot of knocking at idle. That is when they don’t function correctly. It sounds like a machine gun.
It can be due to clogging, wrong injection timing, or wear on the injector nozzles. Some other reasons are as follows.
- When a diesel engine is turbocharged, deteriorating bearings or compressor blades are behind the rattle sound.
- Noise arises at idle due to simple issues like loose engine mounts and exhaust assembly.
Resolving these issues might take extensive professional help or some basic steps, depending on the severity.
Before you seek help from a repair shop, try the steps below:
- Clean up the injector. Replace it if it is worn out too much.
- Change the motor oil.
- Apply anti-friction additives.
- Get the engine hot enough prior to starting. Plug in the engine a couple of hours beforehand.
- Inspect the turbocharger of the diesel engine for dirt or foreign materials. Do a thorough cleaning if you see clogging.
Frequently Asked Questions
The rattling sound is a signature noise issue in vehicles. Apart from the engine at idle, it can come to pass in other situations. While exploring the topic, I’ve found some of the most searched queries and answered them for you.
Why Does a Car Make a Rattling Noise in the Front?
A rattling noise comes from the front of a car when it has a problematic suspension system. You will experience this noise usually when driving over uneven roads, bumps, or potholes.
Why Is My Engine Rattling When I Accelerate?
A broken engine pulley or belt, loose motor mount, pre-detonation, and exhaust system problems are the malefactors behind clunking during acceleration.
Why Is There a Metal Rattling Noise Under Car?
Broken, loose components predominantly create metal rattling noise under the car. Rusty parts and corroded pipes can cause this sound as well. Besides, broken rubber bushing is another possible reason behind the noise.
Closing Thoughts
When a vehicle is idling, it is expected to be more silent than usual. It’s a natural phenomenon in the world of engines. So, any interruption in this quiet moment indicates problems in the engine.
More often than not, this sound means minor issues with the engines. Address them quickly before it’s too late and costs you an arm and a leg to repair.