Adjusting by sound is quite easy, in fact probably easier and more effective than by voltage as normally instructed. I don't take any responsibility for mucking up your setup, but as long as you use a non-conductive screwdriver to prevent accidental shorts, and you don't leave the thing in max current for extended periods of time, chances of causing any damage are low.

(1) Set the printer moving back and forwards a fair distance (say 50mm) at normal jog speed. You can do this by clicking the manual buttons in R-H, but you run out of hands pretty quick - try writing yourself a little g-code script if you're brave and 'print' it...
(2) Wind the tiny potentiometer right down (counter-clockwise). The motors will stop.
(3) Wind the pot slowly back up (clockwise) and listen. You should hear the following:

* Silent to begin with (no current!)
* Ringing at increasing volume, no movement
* Movement starts, clicking noises and erratic motion
* Motion gets more consistent, clicking gets less frequent and eventually disappears
* Rumbling/grinding noise starts to appear, gradually gets louder, eventually becomes a physical vibration

(4) You want to set it somewhere between the clicking going away and just being able to make out the rumbling noise.

Unplugging fans etc. for a quiet environment helps to make things clear.

Bare in mind only a TINY turn would produce results. 1/16 of a turn can give a drastic result.
Also, be sure your X belt has an even tension. If it constantly shifts to a specific side, this could be a cause.

I'd recommend the following in any case (you should be able to search on the forum for more details of any of them, just use google: "site:soliforum.com tune v ref" for example):
* Make sure the x axis rails are appropriately lubricated (thin layer of lithium grease is well regarded)
* Make sure your driver board is cool / well ventilated - adding a fan of some kind (even a desk fan!) is a good idea
* Tuning V-ref for your x-axis (i.e. adjusting the current through the motor so it runs smoothly - too little current will lead to missed steps, and too much current can overheat the driver leading to thermal shutdowns and shifts)