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An engine rattling noise, or a clicking sound in an engine, can spring up from a number of sources. Whether it's engine knocking when accelerating or some kind of spark knock or just a general engine noise, some are more serious than others, but there’s one thing that’s true of them all: it’s never good to leave it alone. 

There are a whole bunch of reasons you might be hearing your car engine making noise. Check out these reasons you could be hearing an engine rattling noise and what you can expect for repairs with these engine problems and diagnosis.

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Engine damage costs are among the highest when it comes to automotive repair. Replacing an engine is nearly as expensive, so often it isn’t worth it to do either.

We buy cars with major mechanical damage, such as engine issues, every day. Find out how much you can get for your damaged car now.

Engine Rattling When Accelerating

Engine Rattling When Accelerating

Belt Tensioner Replacement

As the engine spins inside, the timing belt or chain needs some guidance, especially as the engine revs climb. Engine rattling when accelerating can be a symptom of a problem with this timing belt. There are guides for engines with a timing chain. Both vehicles with a timing belt or a chain have a tensioning system to keep it snug and centered.

Belt TensionerIf the timing belt or chain tensioner loses its strength, the belt/chain has more movement than it should have. This causes engine clatter when accelerating and the engine clicks as it hits the guides. This will definitely be a loud engine noise when accelerating, so it should be easy to notice.

It’s not usually a good idea to drive a long time after you discover the engine making noise for this reason. It’s going to cost around $500 to $1,500 to replace the timing chain or timing belt tensioner. Left alone, the timing belt could skip or break, causing your engine to not run due to engine failure.

Cracked Flywheel or Flexplate Repair Costs

Cracked Flywheel or FlexplateIt’s tough to detect a cracked flywheel because it’s tucked between the engine and transmission. Plus, who would suspect the out-of-sight flywheel or flexplate would be the issue? The flywheel is fastened firm to the engine crankshaft, and the transmission engages it as you begin to drive. If the flywheel or flexplate is cracked, it bends slightly as you accelerate due to torque.

That means it isn’t perfectly lined up, and there’s a rattle or knocking noise that happens under load. It strangely disappears as soon as you let off the gas, and you might not hear it at all on light acceleration.

If the flexplate is cracked, the transmission needs to be removed to replace it. Between parts and labor, you can expect a bill of around $1,200 to $2,000 depending on your make and model. If you don’t deal with it, that engine rattling sound will never go away. You may need to sell a car with a blown engine at this point.

Engine Rattling At Idle

Catalytic Converter Problems

The most common engine rattling at idle isn’t an engine problem at all. What you’ll hear is a clattering, tinny metal noise when you idle.

Catalytic ConverterThe catalytic converter is an emissions control component in your exhaust system. Its honeycomb-style core superheats unburned gases in the exhaust before it leaves the tailpipe. But that core isn’t going to last forever. When it begins to break down, little chunks break off and rattle around inside. It’s most noticeable at idle.

Left unrepaired for some time, the catalytic converter will cause running problems as it gets plugged up, plus you won’t pass a smog test. To change it can get pricey – it could be anywhere from $650 to $1,900 to have a catalytic converter replaced in your car.

Spark Plug Knock 

What is spark knock? If you have an engine pinging noise, it’s caused by engine detonation. What happens is that fuel is igniting before the spark plug fires off. It’s due to excessive heat, poor fuel delivery, and a bunch of other causes too. 

Spark knock usually happens at idle and smooths out when you’re driving, but the condition is still present. In fact, left untreated, this minor noise can cause your engine to fail badly. Because there are so many causes of spark plug knock, the cost to repair it is all over the map. It could be a couple hundred dollars of several thousand to fix it.

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Collapsed Lifters

The engine lifters – small hydraulic parts that open and close the engine valves – need engine oil to do their job. On some older vehicles, these lifters have been notorious for collapsing, which prevents the oil from pumping them up to work the valves. Yup, it’s another problem that causes engine rattling, especially at idle.

It’s a fairly involved job to replace the valve lifters, and it’s best to change the whole set. Repair costs vary a lot, from $470 to $2,100, all because engines are so different in their parts and labor processes.

Engine Noise When Cold

Piston Slap

Piston SlapIf you fire up the engine and you hear a clack-clack-clack right away, there’s a good chance it’s piston slap. A piston moves up and down in each cylinder, fit tightly inside. If there’s a little bit of wiggle room, the piston is going to rattle against the side of the cylinder wall.

Usually, piston slap happens on all the cylinders at the same time. The repair required is essentially an engine rebuild. Again, repair costs are varied depending on the size, style, and purpose for the engine, as well as the extent of the damage. You can expect repairs to be up to $4,500 on most common engines.

Rod Knock Sound

If your car engine sounds like the bottom end is going to fall off, it’s probably engine rod knock. The noise you hear is like a ball peen hammer tapping on a steel plate repeatedly.

Rod Knock SoundWhat’s actually happening is measured in thousandths of an inch. The microscopic layer of oil between the crankshaft and the connecting rod bearings has worn wider than its normal half-a-hair width. The connecting rod slams against the crankshaft every time the piston moves up or down. The impact makes the wear worse too, coincidentally.

When you have rod knock, you’ll need an engine rebuild or replacement. It’s a sign of oil starvation, which means a simple rod bearing replacement would yield the same result in short order. Repairs are measured in thousands, probably from $3,000 to $6,000 on most cars. If you continue driving it unrepaired, eventually a connecting rod will let loose and break the inside of your engine. Can you say, “bad news”?

If you want to know more about blown engines, we have an in-depth guide on blown engines for various makes and models throughout the years.

Engine Rattling When It’s Hot

Low Oil Pressure

An engine ticking noise might seem fairly normal, but it could be an early sign of low oil pressure. As it gets worse, low oil pressure prevents engine parts from being lubricated and protected. It doesn’t take long until it gets much, much worse.

Low Oil PressureLow oil pressure can be caused by a failing oil pump but it’s much more likely it’s due to lack of maintenance. A basic oil change is the main prevention method. If your engine has low oil pressure, engine rattling at idle might be present when the engine gets hot. It’s because the oil is thinner and doesn’t coat parts as well.

Low oil pressure usually means a complete engine job. Either a replacement engine or an engine rebuild – either way, it’s going to cost you big money.

Heat Shield

On the flip side, a common engine rattling noise when the engine is hot is so very minor. On the exhaust system, heat shields prevent hot exhaust temperatures from affecting nearby parts. These thin metal skins are susceptible to rust and corrosion, though. If they begin to rust away, they can rattle and tap, driving you to the mad house.

Heat shields are inexpensive, usually less than $100. They’re still important to replace – if not for your mental health, then to protect engine parts from exhaust heat.

Should I fix my car or Sell it As Is?

Should I fix my car or Sell it As Is?

Don’t Fix It – Sell It

Don’t Fix It – Sell ItEngine rattling noises can be annoying and expensive to fix. Instead of trying to scrape together thousands of dollars for a fix, why not sell your car as it is? CarBrain will give you a guaranteed offer for your less-than-perfect fcar, engine rattling and all.

Simply fill out a request for a quote with your vehicle information. We’ll give you a guaranteed offer. If you accept the offer, we’ll put money in your pocket, just like that. Then, we’ll come get your car from where it sits, and we’ll take care of the towing costs. It’s fast, it’s easy and it’s free to use CarBrain. What are you waiting for? Get your guaranteed offer now.


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