I have a KitchenAid Pro 600 stand mixer, and it makes a loud whining noise which gets louder and ear piercing the faster the speed setting. I did not make this noise when I first got it, just a gentle whirring noise. What might be happening with this machine?

It sounds like the Worm Gear is going out. The faster the motor runs,
the more damages the Center Gear is grinding away the teeth of the
Worm Gear. Things start to slow down, and eventually they will come
to a halt. It's time to replace the Worm Gear. Also make sure to use
new fresh Kitchenaid Food Grade Grease with the new replacement.

your control plate is worn out. it will need replacement.

Counter top appliance number for Kitchen Aid is 1-800-541-6390 M-F 8 - 8 EDT and Sat 12 - 5 p.m. they should be able to help you

Change the speed control board. Repair alot of these

KAY – You don’t mention how long you’ve had your mixer or how intensely you use it, which would be helpful in assessing your question. Our first KA mixer we got in May 1989, seemed ‘whisper’ quiet compared to the replacement 6 qt Pro mixer our children got SWMBO for Christmas in 2006. The new mixer was so noisy that my wife called Kitchenaid to complain. The wonderful KA ‘Helpers’ explained that KA had changed to making all metal gears in their mixer transmissions as opposed to having one plastic gear (intended to fail instead of burning the motor out). That change from plastic to metal is then main reason your KA mixer seems to be much louder. You should be able to judge if your noise level has increased or stays the same during normal use. Since you stated that you don’t notice any overheating of the mixer I would say that the noise level is appropriate and wouldn’t be overly concerned at this point. That being said, if you hear a change in the noise level – usually louder, it could be indicative of mechanical issues in the transmission, which is what finally happened our mixer. One of the gear teeth broke and the agitator froze up. But that is another story…
I hope this helps. Good luck! Howard – Burke, VA
If this solution has helped you, please rate it, thanks!.hslincoln

lgardash, Are you sure it's the motor or could it be the transmission?
It 'sounds' like you've got some transmission gear issues, and a situation similar to my wife's mixer, which we got new in Dec 2006. (Within a week of her first using it, she contacted KA Customer Care and the only 'care' they offered was an explanation that the new KA Pro Mixer gears are all metal and to expect it to be louder than previous models that used a plastic gear (to fail). Well, there's an acceptable level of noise, and an unacceptable level (you don't need to be a mechanical engineer to know when something doesn't sound right) and it seems that my wife's new mixer's operating noise level was always unacceptable. It finally 'died' this past October.) OK I've vented enough on KA... now what might be your problem(s)?
It could be as simple as thorough normal use the gears have shifted slightly in the transmission and the gear teeth are making different contact, hence the grinding/squeaky noise. The higher the speed, the louder, higher pitched sound you'll get. Alas, the noise may also be indicative of a potential gear failure (after our mixers increasing noisiness, the bevel gear broke and the mixer 'froze').
If your mixer is under warranty, contact Kitchenaid. If it's out of warranty, then take it apart and do a diagnostic exam of the gearing. Whatever you find you should be able to fix yourself. Be sure to have the Kitchenaid Part Manual (Part No. 8212278 Rev D) on hand if you attempt to disassemble yourself. It also lists all the parts so that you can determine, which parts, if any have failed. You'd think that the Kitchenaid name would warranty their mixers for a lifetime... So much for quality in America today!
I hope this helps, and good luck! - Howard, Burke, VA

Several things:

The Professional 600 has a metal gear housing with a metal gearing. Because of this, the Professional 600 will generally run louder than other stand mixers that may have a nylon/metal mesh gearing.

How long is the bread dough being mixed for? Kitchenaid stand mixers must be used on speed 2 for bread doughs, using the spiral shaped dough hook, and mixing for no longer than 7 minutes.

If the flat beater is getting caught on the bottom of the bowl, pleasure assure the bowl is being seated correctly. You will place the bowl on the mixer arms on the left and right hand side. You will also want to take your fingers along the back of the bowl, where it butts up against the base of the mixer, and press downward. You will hear an audible click as the bowl falls into a spring latch and allows the bowl to sit flush and secure. If this is not being done, the flat beater may strike the bottom of the bowl.

If this was not the cause of the problem, please consult your Use and Care Guide about the beater to bowl adjustment. This is an easy adjustment made with a flat head screwdriver that can quickly correct the problem of a flat beater hitting the bottom of the bowl.

Hi. These mixers normaly make a lot of noise when in operation. Go to the shop that sold it to you, or any place that has these units on display and ask them to turn on the mixer for a demonstration. If their mixer does not make the same noise, then contact Kitchenaid Customer Service and ask for a replacement under warranty. If this solution assists you, please rate it. Good luck! ricardok45

the company jumped right in and helped me out. impressive.

Unfortunately, the Kenmore mixer sounds louder than freight train due to a poor planetary gear design. I had to take mine back so that the neighbors wouldn't **** me. I hooked up two identical models at the store to get the same, painfully loud, experience. I think I prefer the sound of a bandsaw to the grating noise it produced.