Solved Z artifacts on one side of print

So I printed out a part the other day, and on one side the print looked fantastic. There was no z artifacts and the sides were like glass. But on the other side of the print there were huge ribs. Could this be due to a loose belt perhaps? Pictures:

 

I've done all of the suggested fixes in the "Know Issues and Fixes" thread except the ball bearing and firmware upgrades. The improvements were marginal but I still have quite bad Z artifacts on most prints. I'll try tightening up the belts and checking for any loose bolts.

EDIT: Since the artifacts are worse on one side and 'smooth out' as it gets to the other side, would a loose coupler explain it? Perhaps the one side is more 'squished' because of a loose coupler. I measured the thicknesses and the side with the artifacts is about .5mm lower that the other side.

 

The couplers were secure. There was however a large amount of friction on the left side (same side as the ribbing occurred on - probably a coincidence but who knows) of the smooth rods, so I cleaned them off and lubricated them. The hobbled bolt was very loose to the gear, so I removed the gear and wrapped the nut in some tape to make it fit better to the gear. The belts seemed good.

Right now I'm printing a cube to see if any of the above did the trick. I'll update when its done.

Also, would you recommend doing the firmware modification that disables the steppers? From what I've read it seems like it should work but I don't want it to damage the motors.

 

Alright thanks. On the test cube after lubricating the rods and tightening up some bolts, the ribbing is now on all sides faintly, which is kind of a win . I'll try the firmware update sometime soon.

And thank you again for your help. The printer would have driven me crazy(er) long ago but for the friendly folk on this forum.

Edit: After doing the firmware update and messing with some settings, the Z ribbing is 99% gone.