I listen very carefully and looked up on line many items that may cause it. One thing, along with the knock was a ting like noise. Like tapping on the sheet metal of the machine. I rocked the drum back and forth and could only find a similar nose. Rotating had nothing. At that point I figured it had to do something with the suspension rods. The rod toward the back right side would ever so slightly stick (ball) when rocking the tub then the ball would have a chatter like movement. I lubed up the suspension ball with a polyurethane lube and the knock noise went away. It was a knock. When I pulled the washer from the wall I accidently broke the connector so make sure you disconnect the lines.