My lock is not working on my mixer. Basically, when I am mixing or kneading even a small batch of dough the head of the mixer starts lifting up and down. Has anyone had this problem? How big of a problem is this and how do you go about getting Kitchen Aid's serviced/repaired? My mixer is 2 years old, exactly and before about 3 months ago when I started baking bread I had only made my wedding cake (along with all the test runs!!) and really not much else.