Question regarding KitchAid mixer, Model K45ss.

Yes this indeed does sound like you have a problem. There could be a couple different cause of this noise. If your main drive or worm gear has been damaged, it is likely to not run at all or jam up. So i think this is not the problem. There is however a codder pin located inside the transmission gears this can be seen by removing the upper housing of the unit, and then exposing the oil and gears. clear away the oil surrounding the gears, and save this grease for later. After this you should be able to visually see this codder pin AND the gears, rotate the gears while inspecting them and the pin. If the pin is slightly bent or broken this will make the grinding noise that your are talking about, while still operating and driving the unit. part number for the codder pin is 9705444. If however the noise is coming from the motor area this could indicate a worn or faulty motor bearing. This can cause the motor to operate on an angle and can cause a rubbing noise from the cooling fan or the winding of the motor itself rubbing on the mixer housing. Part number for the braket and bearing is 3180526. both are relatively cheap and easy to replace. If you find and fix the problem be sure to inspect or change the oil as this can often have metal chunks and other particles. Hope this Helps

Thanks