89 420SEL kickdown

[blueeagle289]

This model Mercedes seems to have a kickdown system based on vacuum or electronic status, in addition to the obvious switch on the floor under the accel pedal !? It sometimes comes in when I really don't want it to, either in Cruise Control "Resume" mode -- or when I am accelerating but not trying to set a new speed record. Someone suggested that the vacuum modulator could do this ?? Otherwise, is there some way to reduce the effect of this system or turn it off completely ?? I don't like the "hard clunk" that comes from the tranny and/or drive train when it engages particularly and don't know if that kind of fairly loud mechanical noise is considered normal on that car. Please advise from your knowledge/experience regarding that model.
Thanks, Ben Carter