Y'day I've noticed one stepper motor is making a little sound (like shhhhhhhh

I did,
1. swap drivers - the new driver in the same socket getting hot. So it is not due to faulty driver.
2. swap motors - the new motor making the same sound. So it is not the motor or cable connecting the motor.
3. swap Arduino Uno - problem persists. (giving my luck, I just wanted to make sure something funny is not going on, hence tried that).
Any help highly appreciated!
Thank you
I noticed everything after making my new Electronic Enclosure.
- http://www.shapeoko.com/forum/viewtopic ... =20#p58558
OR
- https://plus.google.com/+rjanapriya/posts/UumxVQvTxjJ