Did you ever figure out the answer to this? I've been using my sister's FW until I got one of my own for Christmas. The new one has a bit of a knock. Not very loud. I almost feel it more than hear it. I am sew new to sewing and sewing machines. Maybe I'm imagining it. But It just seems different than my sister's did. More of a clunk than a knock. Did changing the needle help yours?
Thanks,
Gloria in Kansas City