Whoever said the 727 has a quiet cockpit is full of horsepoopie! It is by FAR the loudest plane I have ever experienced. I flew the C-130, which was darn loud, but we had enough sense to use full earcup headsets and the freak'n intercom. In the 727, there is an intercom, but we don't use it for some reason - we just yell, and yell loudly. Each plane is different, there are some noisey jets, and then there are some outrageously noisey jets. The speed does have an effect on the noise, but the biggest variable is the airconditioning system which dumps the air and noise out just above the S/O's head. Some systems will make you deaf.
Honestly, if I could afford the Bose headset, I'd have it already. I think it would be well worth it on the 727. I personnally wear "ear muffs" from a hardware store for my walkarounds. Sticking your head in the wheel well with the APU screaming with anything less will make you deaf. In the plane, I wear the thick white or yellow ear plugs. I load up on these whenever the company has them out. Quite often they have the cheap/thin earplugs that aren't worth anything. But, like I said, in the plane I wear the thick earplugs. The problem is, quite often you can't hear the guys up front since they are whispering sweet nothings at their windscreens. I simple tell them that if I don't respond, it means I don't hear you - speak up. For checklists, I sometimes find my self reading a step, pausing, and reading the next step - since you can't hear the quiet guys' response.
The moral of this long-donkey story is the 727 is FREAK'N LOUD!
Goose17