Irregularities on the Z axis of prints, but not repeated banding

I am having a rather odd issue with my printer where the layers are not perfectly aligned in an irregular fashion. It is not the traditional z-banding however, for it is not in a repeating pattern. I have some pictures describing the issue. [goo.gl] . I am running a bowden setup with very little friction in the tube. I am using a triple lead screw system with 4 smooth rods for support. The filament is pretty good. Also, a point of interest is that the irregularities tend to decrease, but no disappear at lower layer heights, also, the irregularities seem to go away at certain points of the print and re-appear in others. I am truly bewildered as to what may be causing the issue.

I had a similar phenomenon a few weeks ago: Sudden slight level shifting which disappeared magically and were not repeatable. I had a loose screw at the top of a smooth rod mount. Took me some days to find it ;-) It's worth to take a look.

Thanks, I will look