My AC went out this spring. In Aug I tried it again to varify that I wasn’t needlessly suffering. Ever since then my pick up ( Chevy Silverado 150 ) has a knocking comming from behind where you charge the AC. It will occure for about 30 seconds after turning the key on OR off. I am also getting a low grinding sound ( like an old water wheel or a gear running slow ). This is continual even at an idle. Any ideas? Any conecttion? Thinking maybe compressor or silanoid.