Saw this asked and many wrong answers on reddit.
Packing mags is silent, you turn down interface volume and packing mags becomes silent to you as well, cantr be heard no matter what.
Opening your inventory does make noise, depending on the gun you are holding in my experience.
Every form of movement including turning makes sound even slow crouching, turning even a few degress can cause a shuffle of your feet so there is no way to be silent unless you are standing still.
Reloads can be heard from very far away so be behind good cover with enough distance and saftey before reloading.
SEARCHING BAGS AND POCKETS MAKE NOISE,
searching anything makes noise, if you turn off interface noise you can still here search sounds because it is actually hearable but kinda quite.
Hopefully you learned something and happy ratting!