The fan blades rock slightly sideways in their mounts. At speed, they are obviously tightly supported by centrifugal force (don't start that argument please!), bit slowly rotating they produce an awful racket. The 747 can be deafening. They rock from side to side during the rotation. It's amazing to see the tip clearance from the inner surface of the cowling- as long as they keep clear of that, that's all that matters!