Rippling Effect

Hi, I'm having a problem printing walls (for an enclosure) at certain thickness without getting a rippling effect along the top. The more it prints, the worse it gets and you can hear the head bouncing over the piece. I have had no problems printing other objects, just walls.

I believe it has something to do with the amount of infill getting added. I've tried setting the extrusion multiplier down to .9 to lessen the overall amount of material with no changes.
Attachment 9758

This sample shows wall thicknesses from 3mm down to 1mm in 0.25mm increments. As you can see, some of them are perfect...of course I need 2mm which is 5th one in and is the worst! When it's printing, these are all straight lines so there is no zigzagging with the print head.

I'm using a MakerFarm Pegasus 10", Titan e3d-v6 hot end, Repetier with Slic3r, and 3D solutions PLA filament.

Thanks for your help!

Looks like it could be over extrusion and maybe to hot. Also if the wall thickness is not a multiple of the nozzle size you could have some issues.

what infill are you using ?

As an update, I think I have the settings fine tuned so it's printing properly. Even though I have the diameter set properly, I've had to set the Extrusion multiplier way down to 0.8. I thought maybe the eSteps was wrong but I confirmed with MakerFarm that it should be 102.3.