Last week my 05' F150's AC was not cooling my cabin. I checked the coolant level and it was about 10 lbs. low for the outside temperature. I added the refridgerant and since then the a/c is cool, but not all of the time.

When I start my truck up and have the a/c on, seven seconds later I can hear a sound that sounds similar to my car buffer only deeper in tone for about 2-3 seconds. I tried to narrow down what is making the noise by turning my truck off and on. I found that after I start my truck my low pressure line and the black thing it connects to shakes like mad and makes that grind/squealling sound.

Any ideas as to what the issue is?