Many dishwashers have a part called the macerator or chopper to cut up larger chunks of food before sending the waster stream back to the wash impeller. These are not meant to function as a disposal but to protect the wash impeller from stray chunks of food that may be circulating in the dishwasher. The best way to prepare dishes for the dishwasher is to scrape off all the chunks with a fork and leave the rest. Don't pre-rinse because you'll just create a caustic slurry that will etch your glassware. The chopper is there for the occasional soft chunk of food that made it into the dishwasher by mistake.

Sometimes, the chopper needs to be replaced. This is a fairly common and easy repair on the Whirlpool-built dishwashers. The procedure is similar on LG dishwashers.

Sometimes, you may need to replace the chopper in an LG dishwasher because it's making a weird whistling noise due to a defect in the design of the chopper blade. Brother john63 explains more about this and how to correct it:

<<<Any time the pump is running there is an annoying whistleing sound.>>>

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During the WASH cycle---not the DRAIN MODE---correct?

All LDF6920 dishwashers have a flawed CHOPPER (also known as Macerator).

The CHOPPER has tips on it that are too much like an indian arrowhead tip---which causes noise during the Wash cycle.

A replacement CHOPPER corrects this.

Part Number---> 5832DD4001B

To replace the Chopper:

Remove both racks

Lift/remove the Lower Wash Arm (snaps out)

Remove the *Water Tower/Tube* that runs/routes from the Filter Housing---up the back of the dishwasher---and to the top of the dishwasher.

This done by removing the Phillips screw on the Filter Housing---which has a small stainless steel tab on it.

Then unsnap the mounting tabs (with your fingers or flat screwdriver) of the Water Tube at both---the top/center of the dishwasher and the back/center of the dishwasher.

Pull the Water Tower towards the front slightly---and twist/turn to the right---until it comes out of the Filter Housing.

Use a drill to remove all of the Filter Assy screws

Lift off the Filter Assy

At the rear of the Sump Assy---there will be a round/white Valve---pull it off (re-install the black o-ring if it has come off).

Remove the IMPELLER screw (reverse-thread) and pull.

Remove the Impeller Housing (lift off)

Remove the original CHOPPER and install the new one.

Re-assemble in reverse order (verify that the black gasket in correctly seated before carefully installing the Filter Housing).

Source: LG Dishwasher, Whistling, whirring sound