brake pedal noise on 1996 Volvo 960

when braking recently a noticable sound from the pedal area started. it appears to make the idle a little rough also. the car still stops fine, and no warning lights are showing.i'm looking for air leaks and also wondering about power assist or check valve or possible master is appreciated.

Asked by for the 1996 Volvo 960
This sounds like the brake booster may be leaking. If that is the case it will need to be replaced.
I have had to replace the Brake Booster (BB) on my '96 960 as well. The leak in the BB actually causes a vacuum leak (Manifold vacuum) which will cause a rough engine idle and trigger trouble codes. I decided to replace the Brake master cylinder as well it needed to be removed with the BB; just preventing double work.