A/C compressor makes noise

Removing EPR Valves when Converting Your Mopar to 134a | Classic Auto Air - Air Conditioning & Heating for 70’s & Older Cars & Trucks. found this for you . Makes sense . havent heard your noise so I really don't know what you are chasing ,if it's light then perhaps this valve is cycling rapidly but I have nothing to go on if I can't hear it... Your post makes it sound pretty heavy so I was going that route .
Anyway I'm sending u the link not so much for the noise , just remove it and check . But you will have to eliminate EPR in lieu of installing an AC thermostat at the EVAP to cut comp. operation at point of freezing EVAP. If not installed already .