- low pass filter. Assuming the dust is small compared to the expected movement in the groove, you can filter it out electornically.

- dust detector. Nikon had a cool 35mm scanner... instead of RGB, it had an additional IR layer at an angle just to detect dust. So, automated dust removal tools knew if a black spot in an image was supposed to be there, or if it was actually dust. Here, extra optics would know if the laser was reading dust and could mute/filter the sound during that time.