Linerider,
ALT knob makes ZERO noise... And, just a reminder, every assumption here is ONLY based on CVR recordings. FDR has still not been found.
Through the headset + the aerodynamic noise, you might not hear it, but if the noises are filtered out, then you might hear the sound of knob turning
Knobs were turned 15 times, see the source of this info in my post
here