I have used kydex holsters that have had fabric, usually Cordura, laminated to the exterior of the holster. This is usually done to apply camouflage to the holster but has the secondary benefit of quieting the holster a bit. It deadens the creaks, clicks, and various other noises that kydex holsters can make. Now, don’t run out and glue fabric to your holsters. The sounds your holster makes is probably not really worth worrying about. I only bring it up because I recently came across an interesting new finish that VEIL Solutions is experimenting with – Rhino Lining.
They have Rhino Lined one of their Valkyrie model holsters and I am interested to see what, if any, benefits they uncover in their testing. I suspect that it will serve to deaden the typical kydex sounds but also wonder if it might add an additional level of durability that would come in handy during one-hand manipulation drills. Only time and testing will tell but it is great to see someone trying something new.