When I hit the brake pedal, it produces sound like exhaling air below the pedal. Started a month ago and I am not sure whether it can be described as "hissing". It is literally as somebody loudly exhales. During my oil renewal, the guy checked the brake pads and said that everything is fine. The cars brakes normally. I don't understand much in cars, but the sound makes me tense. Is it dangerous? Do you recognize this issue?   

@Pennypincher_mk I don't know how much you know.

 

What is often described as the "brake servo" is more properly and correctly described as the "brake vacuum servo". As such, there will be an air pressure release associated with the use of the brakes. So possible diagnoses, most safety critical first: all work will be in the same area of the car though:-

1. Has the pedal pressure increased (more force for a given stop) since this started? If so then, you may have a vacuum leak when the brakes are applied. This is potentially dangerous since a servo failure will leave you with an extremely heavy brake pedal!
2. You have a moved piece of wiring conduit or bulkhead sound insulation leading to a noise path from the brake servo to the brake pedal linkage.

Check the servo vacuum pipe. They have been known to crack.

32 minutes ago, TMB said:

Check the servo vacuum pipe. They have been known to crack.

 

I replaced the servo vacuum pipe on both my cars recently, they were both cracked - They are about £33-£39 from a Skoda dealer - They immediately improved the braking system too.

 

When starting one of the cars, the engine seemed as though it wanted to jump out of the engine bay, this also ceased after fitting the vac pipe.

 

DB.