You know there are several things that rotate on the front of your engine.
Air Pump, Alternator, Power Steering , A/C Compressor, belt tension pulley, idler pulley. Any of these can go bad.

Racing the engine in Park is probably not a great idea. If you can hear the roughness from inside the car, then you probably can really hear it and probably locate the source by looking and listening in the engine compartment while somebody else revs the engine.

Steve