I have a KA with the anodized aluminum paddle. If it rubs on the bottom of the bowl while mixing I have that problem. It’s actually really gross. The aluminum being rubbed off into your food is the gray you see, YUCK! You can adjust the bowl height to keep the paddle from dragging on the bottom of the bowl. Another fix is to get a side-swipe beater or similar that is not made of aluminum. Here’s the one I use and I love it!
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