1994 Pontiac Engine Noise

1994 Pontiac Firebird 3.4l 6cyl
119,000 miles

i went to the gas station and put gas in my car, after that i went to get food and all of a sudden when i turned it off, my engine on my driver side started making loud compressor noises (like an air compressor) ignored it, got food, wen home turned it off did the same thing. what is the noise?

thank you