When the noise happens tells you what it is
On an LG dishwasher, the timing narrows things faster than the sound. A grind during the wash means something hard has reached the filter or the sump. A rhythmic tap means the spray arm is striking an item in the rack. A knock as the machine fills is usually water hammer in the plumbing. And because these machines are quiet by design, small noises that another machine would mask are plainly audible here - which is not always a fault.
What you are seeing
- A grinding or crunching sound during the wash.
- A rhythmic tap or knock while the machine runs.
- A knock in the pipework as the machine fills.
- A hum that continues after the cycle has finished.
- Not this fault: A short hum during the drain is normal.
- Not this fault: Water rushing at the start of a fill is normal.
Most likely causes, in order
- Something hard in the filter or the sump — Why ranked: First because it produces a grind that continues through the wash, and because leaving it there damages the pump.
- Spray arm striking an item in the rack — Why ranked: Second because a rhythmic tap has no other explanation, and it costs nothing to correct by reloading.
- Water hammer in the supply line — Why ranked: Ranked here because it arrives only at fill, which separates it from everything that happens during the wash.
- Drain pump labouring against a restriction — Why ranked: It makes its noise only during the drain, giving it a timing signature of its own.
- Wash motor or its bearing worn — Why ranked: Last. It is the most expensive answer and it presents as a constant noise at every stage rather than an intermittent one.
What to check, in order
- Note exactly when in the cycle the noise happens. — Because: Timing separates all five causes faster than the character of the sound does.
- Twist out the filter and look and feel for anything hard in the sump. — Because: Rank one is the commonest finding and needs no tools.
- Spin each spray arm by hand and check nothing in the racks blocks it. — Because: Rank two is confirmed the moment an arm catches on something.
- Note whether the knock arrives only as the machine starts to fill. — Because: That timing points at the plumbing rather than the machine.
Checks you can do safely
- Run a cycle and write down exactly when the noise occurs - fill, wash, or drain. — N: 1 — Tools: Notepad — Time: one cycle
- Twist out the filter, rinse it and feel carefully round the sump for glass or hard debris. — N: 2 — Tools: Gloves, torch — Time: moderate
- Spin each spray arm by hand through a full turn and move anything that catches it. — N: 3 — Tools: None — Time: quick
- Reload the machine so nothing hangs through a rack, and run the same cycle again. — N: 4 — Tools: None — Time: one cycle
- Stop rule: Stop here. Removing the pump cover, the spray arm assembly or the motor is service work.
Before you reach into the tub
Safety
Switch off the dishwasher breaker before reaching into the sump. A capacitor can hold a charge after the power is off. The water in a tub can still be hot at the end of a cycle. Broken glass in the sump is common; use gloves and a torch, not bare fingers. Never run the machine to test while the pump cover is off.
When this becomes a service call
A grind continues with the filter and sump confirmed clear. A hum continues after the cycle has ended. The noise is constant at every stage of the cycle. Any burning smell during a cycle - kill the breaker and stop.
Nearest pages
What this page does not cover
This is generalized information for LG dishwashers as a group. It does not separate motor designs by model or name parts. Where a family- or model-specific page exists it supersedes this one.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
