If your dealer is the one telling you that's normal then you need to find another one. If you contact Viking they can recommend someone in your area. I'm not sure on the Diamond but even my Viking #1 had a sensor presser foot and would adjust for thicker fabrics; my Ruby has it so I know they are still doing it. Have you changed your neelde and oiled it(if needed) I know that my machine makes quite a noise when the needle starts getting dual. Also use a vacumm and blow out the bottom. My Ruby says don't blow into it because you can make the dirt go into the machine deeper.