Knocking when AC is on.
 

So when I am idling with the AC on, there is a loud knocking noise. It only happens with AC on, when AC is turned off it goes away. If I push in the clutch the knocking stops. Any ideas on what this could be?

This is just a normal occurrence, the engine is working harder with the ac/defroster, i have the same thing with my 2009 tC, just don't hit the gas hard with the AC on, that will cause more damage.