Sorry about delay. (I was waiting for an email.) Yes, when we turn arm by hand it does hit back wall. When washer operates, we can hear the knocking, but when we open the door, it stops.
Thanks for you help. No, the back of our dishwasher isn't bowed. Yes, the video is easy to follow, and the DW is just like ours. No, we didn't do the project today (too late and too busy).
Is there a way to give you feedback tomorrow? We'd like to tell you how our DIY project worked out.