It's possible that the laser assy may be scratching your discs but I've never seen that occur. The laser assy starts reading the disc from the center out so all the scratches would be concentrated near the center of the disc. It's also possible that the previous owner may have lodged something in the unit and it has shifted position and now is scratching your discs. More likely is the fact that the disc is spinning and rubbing against the plastic tray rather than riding on the spindle motor. The spindle motor is what spins the disc and if the disc is riding on the plastic tray rather than the spindle motor lower plate you may hear a whirring or grinding noise. If such is the case, more than likely the spindle motor lower plate has shifted position and has dropped below the plastic tray. This plate is tightly clamped to the disc by another top mounted plate and a magnet. If the bottom plate is too low the disc will spin freely on the tray. Do hope this helps, Eric