"wooshing" noise while pressing on brake pedal

[grubsster]

Hi all,

I am currently wondering what could be causing a "wooshing" noise as I press on the brake pedal. My brakes seem to function well. Front disc / Rear drum with proportioning valve. There are times that it does not make the noise, but lately pretty much hear it all the time. I'm thinking a bad booster but, don't want to break out the parts gun.

thanks for any advice.