Kitchenaid mixer motor makes loud grinding, squeaking noise.
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