What causes High pitch whistle when dishwasher is running

SOURCE: LG dishwasher is whistling a high pitch tune

It is difficult to be specific without knowing the model number of your LG dishwasher.

On newer LG models, the most common cause of noises is from debris stuck in the lower filter assembly area. Recommend you remove the lower spray arm and the screws that holds the filter sub-assembly in. After removing the assembly, inspect with a flashlight to search for any debris that is jammed in that area. Also rinse out the filter as best possible to remove any thing you see in there. Reassemble and test.

SOURCE: Our LG LDF7920st dishwasher (6 months old)makes a whistling noise

Hey, consider the float assembly!

We bought this dishwasher and ran it for the last 1 1/2 months and it made a grinding and whistling sound from day one (it's supposed to be nearly silent in its operation). Turns out the drain pump was cutting in while the machine was still filling, thereby emptying the wash tub of any water. Then, when the cycle proceeded to wash, the dumb thing had no water and made a horrible noise. So I had to pitch in at least 2-3 litres of hot water, and then it worked quietly! Had to do this every time there was new water intake.

After working with the repairmen - four visits later, we isolated the float assembly as the problem and they set about replacing the part. Turns out the two parts were markedly different. LG HAD INSTALLED an older model float assembly at the factory and it was the problem. The replacement part was the correct float assembly and things worked perfectly after that - thank goodness. No more babysitting the dishwasher.

Don't let anyone tell you the motor assembly needs replacement. I have seen that cop-out 'fix' all over the web. But use deductive reasoning to find out where the problem is in the cycle, and explore this option first - it's a quicker and cheaper fix than replacing the whole motor assembly.

'Mr. Float' as he is now called works like this:
-expels any residual water in the tub from the last wash
-intakes water for the wash or rinse
-whirs 2-3 times prepping for the cycle
-begins to wash, quietly
-expels at the end of the wash or rinse.

He used to:
-expel residual water
-intake new water for wash or rinse
---drain pump would cut in WHILE still filling
-machine would whir once, realize it didn't have enough water
-perform a brief top-up intake shot
-begin to wash and whistle and GRIND (this is where I would have to add the water)
-expels water from wash or rinse, and start all over again.

It's a good dishwasher and it will work, but the right model parts have to be in place!

SOURCE: High pitched whistle

First a suggestion...try this guys solution with the impeller blade or ordering a different part. http://forum.appliancepartspros.com/dishwasher-repair/318842-high-pitched-squel.html
Now the rant...NEVER BUYING AN LG ANYTHING AGAIN!!!! Just talked to LG customer service they are worthless. I have the LDS5811 with the same problem. If you aren't going to man up and back your product when there are major flaws I don't want to buy from you. I have spent 250 bucks servicing this unit and it is only 4 years old RIDICULOUS. LG you better get your act together. I am not going to buy another LG appliance unless they start owning up to their faulty manufacturing. This dishwasher was not cheap when I bought it and has been nothing but a head ache. First the wiring harness got loose and shorted the board, because they embedded the wiring in the insulation in the door. Now this stupid noise that tortures any animal within a mile. My home warranty won't fix it "till it breaks." Back into ear purgatory my family goes till I can get this part.