WHAT CAUSE A RATTLING SOUND WHEN YOU TURN ON YOUR AIR CONDITIONER

Thank you and well done for narrowing down the symptoms. Does the noise sound from inside or outside of the car? It could possibly be a noisy compressor or a power steering line rattle against one of several brackets, when the rpm rises as A/C is selected. I have had other things causing rattles such as the tensioner and pulley assembly which was only heard with a/c on and applying slight load such as putting in D and turning the steering wheel. Also possibly the A/C compressor tensioner and pulley assembly or the fuel vent line can also create a rattling types noise at a certain RPM. Good luck