Filastruder black tube moving

Hello, We finally got our filastruder put together after many attempts and now when we turn on the motor, the black tube gently moves up and down, not a lot but enough to notice. We thought at first that maybe our tube was not screwed in tight enough to the wood block, but we tightened and loosened and tried to adjust the position of the feed screw, but it still moves up and down. We know that this can't be god, but we can't figure out why this happens and thus cannot come up with a solution. Any one else have this issue? how did you solve it?

thanks

Lorena