Have the condition of your engine / transmission (mounts maybe even mounting hardware) inspected.
They may be deteriorated or something broke or has come loose and maybe allowing the engine/ transmission to torque (move) out of the boundaries it was meant to stay within.
The air conditioner's shaft/ belt/ pulley may be contacting the inside of the car body while it is turning. Hence the grind/ racket you are experiencing!
Lifting the hood and staying to the side (not front!) Of the vehicle, while someone else holds the brake pedal down and Mr. Parking Brake is "on", while shifting slowly from Forward and to Reverse, might let you see the "Over-Torquing" of the engine and if the air conditioner is on, you may be able to see what is contacting and grinding.
Please stay away from the front and rear of the car while doing this!
Do not do this near another vehicle/ etc!
Just trying to look out for you!
Return with news of what you find!
The Medic
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Sunday, July 3rd, 2016 AT 9:28 PM