And I guess that a delta machine is always noisier than a Cartesian printer because it runs all 3 motors all the time. I think the firmware has some kind of an impact. I remember that the Prusa MK2 has different run modes in the firmware settings that impact the noise level. Running the motors in the low power mode makes the printer very quiet. I wonder, if that can be done on a Rostock, possibly by using Marlin instead of Repetier.