Is it mechanical or magnetic? In other words: is it a grinding feeling or just a spot the spindle 'likes' to be in?
While trying to troubleshoot my original, ailing vector drive, I learned that the vector drive carefully regulates its output when the spindle is running. When it's supposed to be off, there are also idle voltages coming out that are not always equal. You can sometimes feel that as a spot the spindle tends to favor.
I guess a way to test would be to e-stop the machine. That cuts power to the vector drive. If it still has that feeling, it ain't electronics. Write it down though. And get it documented. The VF-2 comes with a 1 year warranty, right?