I didn't feel any urge to yell or scream or anything ... I think it was mostly a quiet birth. I just did what felt natural throughout the process (I did ask the nurse at one point if I should be shifting breathing techniques since I'd gone on to the "next" stage, and she said, "If it's working for you, why change?"
). She also told me that some of the other nurses were wondering if I realized I was in labor.
DH says I moaned "a little" while pushing. I can actually remember the sounds of the nurses setting up in the corner while I was in active labor, so I must not have been very loud ...?
I think it depends on the mom. I bet the "noise" scares the staff (worrying that you're going to get out of control etc.) -- and therefore they think by squelching the noise, they'll be preventing mom from panicking. Kind of like putting a bandaid on a sprained arm and thinking it'll help.
I was fortunate, the OB and hospital staff were really great with us. It probably helped that I was certain of my plan, and had a relatively quick labor (arrived at 12:30, birth four hours later). A lot less time to 'interfere.'