newone---did you use the steel shaft or the carbon one??? I use the old version of the mod with the airline tubing like the one in the video. But I used the steel shaft as it is just a little longer and extends into the hole on the centering cap of the shroud.
Then after a while of the noise I thought of cutting about 1/8-3/16 of the black airline that comes with the maxi-jet and I glued it into the hole in the center of the cap, so that the steel rod slides into it.
absloutley no noise at all.
also i dont use the stopper, If it starts the wrong direction, I just stick my finger in it and hit the prop and it goes the right way....(trust me it doesnt hurt...) But i leave mine on all the time now so it is no big deal. I say this because it sounds like your prop may be hitting the stop rod so it is not spinning.
hope this may help ya out