Yes thats another another one that ive come across, but not as often, the rubber disk the CD sits on loses its grip, and the disk slips, you can here it when that happens, the isoprophyl alcohol removes contaminants from the rubber plate / washer, it does mean opening up the unit, so i would clean the laser lens at the same time with the alcohol and a lint free soft cloth, then if it continues its probably a component fault, or software. But rule out the obvious usually does the trick.