What sort of pulley system do you have ? What size is it ? You can only go down to a certain size before needing to machine the snout.
Your problem sounds weird... it may be the pulley has worked loose and is moving back and forth on the shaft... but the original pulley is press fitted with over 30ton of pressure.
Is the shaft moving in and out with the pulley also ?
There is an inner spring which pushes the other end of the shaft into the coupler on the blower vane gears inside the housing. If that spring has broken that may explain the in and out movement. But you would see the shaft moving in and out of the housing if this were the problem...also the coupler is likely to need replacing if this is the case.
see
here for a pull down shot of the blower snout to see what I'm talking about.