It depends on the positioning of the springs inside the cylinder which rub on the wall of the same. I had the same problem on the Courtois 165, not a big deal, but annoying. To get around this, I bent the spring slightly to one side and looked for the position that made it silent by turning it from side to side or turning it upside down, not that it was a great system but, at the time, the only one that came to mind . Steven Mead's springs could be the solution having a double conical shape with a Teflon coating. I've had them on my Prestige for a few years and I must say they are a great product.
2007 Besson Prestige 2052, 3D+ K&G mouthpiece; JP373 baritone, 4B modified K&G mouthpiece; Bach 42GO trombone, T4C K&G mouthpiece; 1973 Besson New Standard 3 compensated valves, 3D+ K&G modified mouthpiece; Wessex French C tuba, 3D+ K&G modified mouthpiece.