Andrew,
I'm probably sticking my nose in where it should'nt be, but thats pretty
normal.
I have just fitted the Orion Accufocus Unit to my scope and they are great, very smoth, no noise at all, and no vibration at all.
It is unfortunate that there is no clutch arrangement, but to get around that i leave the two grub screws loose, and you can then use the hand control nobs as you always did, as the shaft just spins inside the cupling.
When you want critical focusing, use the allen key supplied and one quick turn of the grub screw and away you go, it only takes a second to do.
Works fine with me, but it's only a suggestion.
Leon