Reply to VCI knob damaged?

Hi Guys,

I have a problem with my vci.
anytime I want to change an effect by holding Shift und turning the 4. effect knob the music starts getting slower and I hear crackles and so. The CPU-usage stays at about 30 %. The knob itself works fine, when I change the effect ammount, the problem starts only in combination with Shift. The other knobs + Shift work perfectly.

any hints??

Edit1: I believe I posted in the wrong section...