1950s Rush of air noise when applying brakes

[dn010]

Can anyone tell me if I should be hearing a very loud momentary rush of air from my booster every time I hit the brakes in my 57? Per the manual, I know a momentary "hiss" is supposed to be audible only with the hood open but this rush of air is loud enough to be heard with hood closed, windows up, fan on high and probably even with the radio going too. It almost sounds the same as when one opens the valve on an air compressor to allow the air to fill the empty compressor hose. I'm also periodically getting a loud vibrating noise from the booster when it's in the "holding position" so I'm guessing the dam thing is failing again. I tried to search for videos of the noise it is supposed to make and am surprised there are none.

[TJ Hopland]

What you are describing does not sound Cadillac like so something has to be wrong.  57 is the hydra vac system?  I don't think I ever worked on any of those, treadle vac I think is what I dealt with.

[dn010]

1957 is the hydrovac system. It was never this loud before so I wanted to verify prior to ripping it out of the car for what will seem like the millionth time. It could just be me but I also feel as if I'm putting more effort into braking which would mean less power assist. I suppose I know what I'm doing this weekend.

[TJ Hopland]

I'm curious how these worked so of you do post some pics and details at least one person will be looking at them.