Sluggo said:
Are you saying it was a deliberate creative decision?

I have no idea. I'm just saying that it occured to me that they had to have gone out of their way to turn on those fans when they were shooting closeups of Vader's face. Maybe they were hoping the cape would be seen in the background of the shot, but having that fan on and trying to hear Prowse through the helmet had to have been hard. They might have done it for secrecy, as no one could really listen in on the "Obi-wan is your father" line being delievered.