#1
when i decrease the volume to 0 there is no sound,
but my i start to increase the volume.i get a lot of feedback
and the volume is soft

my guitar has i volume with a 3 way switch
#2
try replacing the hight ajusting screws with rubber studs or any thing but a conducor ive herd that may lead to feed back and if that doesnt work i may just be you amp or knobs??