Hobart A200 intermittent grinding sound.
I just purchased a used A200 that was used for icing by a Tim Hortons franchise until they switched over to pre-mixed. Then It sat, only occasionally used for mixing cookies.
The machine is making a intermittent grinding sound when under load (mixing dough) Simular to http://www.thefreshloaf.com/node/9769/anyone-familiar-hobart-20-qt-mixers 
But all the speeds work on mine. I don't really want to pull the machine apart if it's not serious.