VPI Synchronous Motor Hum problem

Well, you could always move the belt to the larger 45 rpm pulley by hand if all else fails...

Try moving the unit away from your preamp and keep it far from your interconnects, especially the connection from the turntable to the phono preamp stage.

Have you called VPI? I have this drive and have not had any problems, but it's in an area that it would be difficult to resonate in. Any issues I have had, have been dealt with very promptly and professionally by the people at VPI. If you haven't called them, you should because they are more likely to have seen or heard of this problem before and likely have a solution.