Here’s an Instructable by GYRO: Becks beer bottle with an audio recording scratched on it
We ground a high-speed steel cutting tool which we polished to mirror finish resulting in a very quiet cut, all this taking place under a microscope!
We also have a couple of sapphire tips which we used for some test cuts but we found the steel one are quieter but with a much shorter life, in fact any contaminants in the coating would take a microscopic chunk out of the tip effectively destroying it!
Heating the tip by winding hair-thin NiChrome wire and passing a current through it resulted in a smoother cut, requiring less downforce and reduced surface noise as it helps it glide through the surface without tearing the substrate.
Via Hacked Gadgets.
Check out the video after the break.