Home Blog Mower deck making loud noise -How to fix

Mower deck making loud noise -How to fix

by Jackson White

Lawnmowers are expensive machines so you want to keep them in good working condition for as long as possible. You can extend the life of your mower of you if you service it every year in the spring before the mowing season.

However, even after paying careful attention to your mower, some things can eventually go wrong. One of the problems you might face is your mower deck making loud noise. Some of the common reasons could be your mower has a loose blade which will create a loud rattling noise, you just need to tighten or replace the blades. There could be a build-up of grass and debris under the deck and on the blade making loud clanking noises in which case you clean under the deck and apply some lubricant to prevent build-up.

Lawnmowers make a lot of noise that’s why you need to wear protective gear all the time when mowing. However, you need to distinguish between healthy and unhealthy noise. If your mower is making unhealthy sounds, it could cause more damage to your mower and since there’s no one single cause, we’ll look at some of the reasons why your mower would make loud noises under the deck.

Common causes of loud mower decks

Loose blade

This is one of the most common causes of noisy mowers. When the blade is loose, it will keep rattling as the mower moves. Sometimes the blade can be bent or damaged which can cause it to make loud noises and put a lot of strain on the drive shaft.

You can fix it by first disconnecting the spark plug wire and turning the mower off before lifting the mower on its side. Use a wrench to check if there are any loose bolts. If the bolts are loose, use a piece of wood to jam the blade then tighten the bolts. If the blades are out of balance, use a blade balancer to balance both sides or if the blades are badly damaged, you’ll need to replace them.

Loose belt

A loose drive belt could also make loud screeching noises when you start your engine or when cutting grass. This means the belt connecting your engine to the mower deck which makes the blades to spin is loose and may be stuck between the guides.

If the drive belt has slipped, you simply put it back in its place but make sure you don’t leave this problem unattended because a drive belt that isn’t aligned properly between the guides will wear down and break and need to be replaced.

A buildup of grass and debris

If you mow wet grass frequently, with time grass and debris can build up under your mower’s deck and also the blade. This doesn’t leave enough room for grass to circulate under the deck. This buildup will also deflect the blade as it spins making it to produce a clunking sound under the deck.

To fix it, you can either use compressed air or soapy water if you can clean the deck. First, remove the spark plug wire and tip your mower on its side. If you should use water on your deck then use a pressure washer to loosen the grass and debris, but if you can’t use water, remove the grass and debris with a scrapping tool or compressed air. Once the deck is clean apply some WD-40 on your deck to prevent any more buildup.

Irregular change of engine oil

Although a mower engine is small it still needs regular oil changes, at least after 30-40 hours of use or twice a year. The engine oil helps to lubricate different parts of your mower’s engine and with time, friction and heat can burn the oil and after some time the engine oil stops lubricating your engine as it should. This causes the moving parts of your engine to rub together making a loud noise when it’s running.

To fix it you should change your engine oil at the beginning and during the mowing season if the oil has a dark color or if your engine is making noise. You first warm up your mower’s engine to allow the oil to flow easily. Place a container under the oil fill to drain the old oil then tip your mower on its side so the oil fill cap is facing downwards on the container. Remove the fill cap and allow the oil to drain then return your mower to its normal position and pour the correct amount of fresh oil into the engine.

Shaft bearing

If the shaft bearings haven’t been oiled for a while, they could produce some sounds when they rub against each other as the blade turns.

The shaft bearings are the top of the shaft and to oil them you need to remove the cover and add some oil to stop the screeching noise.

Damaged mower muffler

A muffler helps to suppress the sound from your mower’s engine exhaust and the noise from your engine. If the muffler gets damaged or it’s not properly sealed with your engine, it won’t suppress the noise from your engine properly. Most mowers come with an easy to remove muffler that is cheap and easy to install so it’s better to replace it instead of trying to fix it when it gets damaged. It’s very easy to replace a muffler.

To fix it first ensure your engine isn’t hot. Wear protective work gloves and loosen the muffler by turning it anticlockwise till it comes off. If the muffler is stuck, use a pipe wrench to unscrew it. If the exhaust pipe is damaged, you’ll need to replace it too which might be difficult and you might need professional help. Go with the old muffler to the hardware store to get a similar new muffler. Screw in the threaded side of the muffler into the exhaust until it’s tight.

Types of mufflers

There are 2 types of mower mufflers including reflective mufflers or resonators and absorptive mufflers.

Reflective muffler

A resonator is designed to kill engine noise using acoustic engineering where sound waves are pushed through perforated baffles found in the resonating chambers where some of the noise is canceled out. A specially made resistant material is put between the chambers and exhaust outer casing to further suppress the noise. The larger the muffler the quieter the engine, however, this muffler restricts the flow of gases which causes back pressure that reduces the power of the engine.

Absorptive Muffler

This is a basic muffler that can fit in your mower and doesn’t use clever engineering and does a poor job of reducing noise. It uses a mesh screen that catches sparks that might exit the engine. It doesn’t restrict gas flow which is good for power.

Other common noise sources

Blade spindle
Bolted to the deck and have bearing at the top and bottom. Bearings can wear out which will call for the replacement of the entire spindle
Fitted to the driving belt and if it’s worn out, one or more pulleys are worn out
Spray the bed liner to reduce the sound and protect the metal under your deck
They seal the muffler to the engine and when it breaks there’s a lot of noise and fumes. It’s very easy to replace


There are many reasons why your mower engine will make loud noises under the deck. All you need to do is identify the cause and find a way to fix it either by yourself or with the help of a professional.

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