Rotating the control to get rid of the scratchy / gritty sound is a temporary fix at best. The problem will return as all you've done is loosened the dirt / corrosion that was between the wiper and the resistive path of the potentiometer. The "grit" is still inside the pot and will find its' way back between the point of contact on the wiper and the resistive path. The only long term solution is to thoroughly flush out the control good enough to remove the grit from inside the pot or to replace the pot with a new one.
As a side note, it is always a good idea to rotate controls, flip switches, etc... on a regular basis, especially if you don't normally use them. This helps to minimize the potential for corrosion to set in and bind up / seize the control or switch. If the control has multiple detents, it is best to click into each position and let it rest, then move to the next position. Doing this several times in each direction will help to break up any grit / oxidation that may have accumulated. Hope this helps.... Sean