Noisy Y axis

I finally got my C-Beam machine up and running. After a short while during alignment/testing, I noticed a weird noise coming from my Y axis. The X and Z axis are smooth and "quite". The noise sounds like kind of like a squeak or binding maybe, hard to describe. So far, I have checked to make sure the base runs smooth on the rails. The lead screw is not to tight between the ends. The flexible coupler has space to move, and I have oiled the lead screw.

Could it be the...

Noisy Y axis