From Frankie and Johnny, when Johnny made love with Cora, he said "I trained myself to do it quietly. I've been to places where full-throated orgasm would be highly-inappropriate." I know he was in prison, but what does he mean?
That is just it, he was in prison. If a convict were to masturbate and orgasm noisily, chances would be very good that he would then be .... requested .... to perform on other convicts.
If you are dominant, you'll be the one doing the .... requesting.
If you are submissive, or subservient, or not in a gang, prison either makes one celibate, or quiet, or someone's bitch.
A good movie example of this phenomenon is Shawshank Redemption.