Printing issue: consistent pattern to deformation in layers

[ssv102]

When I print I get a a slight shifting in the layer but the shift is at a consistent distance 2.5mm. I've attached a picture where you can see what I'm talking about.
Things I've tried:

• Rotating 90 degrees to rule out issue with the x/y axis belts
• Adjusted extruder temperature up and down
• Oiled the Z axis lead screws

Nothing has eliminated the issue.
Any thoughts or suggestions would be greatly appreciated!