The short answer
Most noise complaints on a Cosmo dishwasher come from the load rather than the machine: an item touching a spray arm, a light dish resonating, or cutlery moving in the basket. Once the load is ruled out, the next suspect is something hard that has reached the sump. Both are owner checks and neither needs a part.
What you are actually seeing
- A rhythmic knocking that matches the spray arm turning — Means: on-page
- A rattle that changes when the racks are reloaded — Means: on-page
- A grinding or crunching from the base of the machine — Means: on-page
- A humming that is louder than it used to be — Means: on-page
- A thump when the machine changes step — Means: on-page
- A loud bang in the pipes when the machine fills — Means: different-fault — Go to: cosmo-dishwasher-water-leak
- A buzzing with no cycle running — Means: different-fault — Go to: cosmo-dishwasher-electrical-safety
- Body: Match what you see before you take anything apart. A rhythmic knocking that matches the spray arm turning. A rattle that changes when the racks are reloaded. A grinding or crunching from the base of the machine. A humming that is louder than it used to be. A thump when the machine changes step. Some near-miss symptoms belong on a different page: A loud bang in the pipes when the machine fills points at water hammer in the house plumbing rather than the appliance, covered on cosmo-dishwasher-water-leak; A buzzing with no cycle running points at an electrical fault, covered on cosmo-dishwasher-electrical-safety.
Causes, ranked for this machine
- An item in the rack fouling a spray arm as it turns — Why this rank: First because it produces the most alarming noise from the most trivial cause, and because a tall item in the lower rack is the classic case
- Light items or cutlery moving under the spray — Why this rank: Free to fix by reloading, and it explains a rattle that changes from load to load
- A hard object that has reached the sump, such as a cherry stone or a piece of glass — Why this rank: A grinding or crunching from the base is this until proven otherwise, and leaving it there damages the pump
- The machine is not level or is touching the cabinet, transmitting normal vibration — Why this rank: A built-in machine in contact with a cabinet side turns a hum into a rattle
- A worn wash pump or spray arm bearing — Why this rank: Last because it needs a part and because the four above account for most of these calls
- Body: Ranked for a built-in kitchen dishwasher with an electronic control, a manual filter and a drain hose running to a disposer or an air gap. Most likely: An item in the rack fouling a spray arm as it turns. First because it produces the most alarming noise from the most trivial cause, and because a tall item in the lower rack is the classic case. Next most likely: Light items or cutlery moving under the spray. Free to fix by reloading, and it explains a rattle that changes from load to load. Third: A hard object that has reached the sump, such as a cherry stone or a piece of glass. A grinding or crunching from the base is this until proven otherwise, and leaving it there damages the pump. Fourth: The machine is not level or is touching the cabinet, transmitting normal vibration. A built-in machine in contact with a cabinet side turns a hum into a rattle. Fifth: A worn wash pump or spray arm bearing. Last because it needs a part and because the four above account for most of these calls.
What to check, in order
- Reload the machine so nothing stands tall enough to touch a spray arm
- Spin both arms by hand and check they turn a full circle without contact
- Switch off at the breaker and check the sump under the filter for a hard object
- Check the machine is level and not touching the cabinet sides
- Body: Each check rules out the causes above it. First, reload the machine so nothing stands tall enough to touch a spray arm. Second, spin both arms by hand and check they turn a full circle without contact. Third, switch off at the breaker and check the sump under the filter for a hard object. Fourth, check the machine is level and not touching the cabinet sides.
Checks you can safely make yourself
- Spin the upper and lower spray arms by hand with the racks loaded, checking that neither touches an item as it turns — Tools: none — Time estimate: a few minutes
- Reload with tall items laid down and light items secured, then run a short cycle and listen — Tools: none — Time estimate: a quarter of an hour
- Switch off at the breaker, remove the filter and look into the sump with a torch for glass, stones or bone — Tools: torch, gloves — Time estimate: a quarter of an hour
- Check the machine is level and that the door and sides are not touching the cabinet, adjusting the feet if needed — Tools: spirit level, spanner — Time estimate: half an hour
- Run an empty cycle and listen: if the noise disappears, the load was the cause — Tools: none — Time estimate: one short cycle
- Body: Checks an owner can make with the machine switched off at the breaker, or by watching a cycle. Step one: Spin the upper and lower spray arms by hand with the racks loaded, checking that neither touches an item as it turns. Tools: none. Time: a few minutes. Step two: Reload with tall items laid down and light items secured, then run a short cycle and listen. Tools: none. Time: a quarter of an hour. Step three: Switch off at the breaker, remove the filter and look into the sump with a torch for glass, stones or bone. Tools: torch, gloves. Time: a quarter of an hour. Step four: Check the machine is level and that the door and sides are not touching the cabinet, adjusting the feet if needed. Tools: spirit level, spanner. Time: half an hour. Step five: Run an empty cycle and listen: if the noise disappears, the load was the cause. Tools: none. Time: one short cycle.
Safety first
Safety
Switch off at the breaker before reaching into the sump, and wear gloves: a hard object in the sump is often broken glass. Do not run the machine with a known object in the sump, because it will reach the pump. Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off. unplug-before-service
Where the owner fix ends
Call a technician when the machine runs an empty cycle with the same noise, the sump is clear, the arms turn freely and the machine is level and clear of the cabinet. A grinding that survives all of that is the wash pump or an arm bearing, which is behind the lower panel.
Nearest pages of the same kind
Generalized information
This page is generalized across the Cosmo dishwasher line. Front-control and top-control machines, and panel-ready and stainless fronts, share the ranking above but not every part, and this page does not cover a specific model or control revision. Family- and model-specific pages, where they exist, are linked below.
Links: - [Common COSMO Dishwasher Problems](/blog/cosmo-dishwasher-problems) - [COSMO Dishwasher: Does Not Clean or Dry](/blog/cosmo-dishwasher-cleaning-performance) - [COSMO Dishwasher: Controls, Display or Error Code](/blog/cosmo-dishwasher-control-fault) - [COSMO Dishwasher: Cycle Will Not Run or Complete](/blog/cosmo-dishwasher-cycle-fault)
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
