X3 Spindle Motor Noise

[mikemill]

I had a problem with the computer running my X3 with Mach, swaped to another computer but the noise from the spindle motor did not sound right, very rarspish checked belt and had a good look around nothing mechanicly wrong.
Fixed origional computer and run the X3, motor sounded fine as it was before.
While there is no on going problem I am intreged to know why two different computers would cause a motor to run strangely.
Anyone got any thoughts on the matter?
Mike