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My car has a weird noise that disappears as soon as you press the brake pedal. When you lift it the noise reappears strongly and then fades slowly. I have a link to a video video showing this noise.

Here is a plot of how the sound level evolves with time dependent on whether the brake pedal is depressed or not

Edit: The car is a Volvo V50 2005 160.000Km 2.0D Diesel

  • I understand that it sounds like this even if you're not moving, just standing still.. To me it sounds like a vibration of a spring, or a "sissing" noise from air leak at brake booster... But weird, never heard this. I would start the engine, open the bonnet, and stick my head everywhere to hear where exactly the sound comes from - brake pedal, brake booster (where the master cylinder is located), brake caliper.. Try brake pedal first.. – Arturs Bolsunovskis Jul 12 '16 at 17:22
  • What is the year/make/model/engine/mileage of the vehicle in question? – Pᴀᴜʟsᴛᴇʀ2 Jul 12 '16 at 21:36
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If the car is running

If the noise is "clacking" and the car is running, it is typical when the break pads or shoes are worn, there is dirty in the calipers or drum preventing the system to be relocated correctly to the right position for its elements (pads, springs, pins, etc), the break pistons are applying force to the pads/shoes but then leaving too much gap between them when released.

It may also be a slightly bent disk or oval drum, adding vibration to the system. What makes the noise is commonly the pads/shoes hitting their pistons or the retaining pins. When you press the pedal, the pads/shoes gets against the disk/drum therefore the system elements kinda tights in together and the noise disappear. If aside the noise you can sense some vibration in the pedal, even just almost un-noticeable, then the disk/drum are bent for sure.

If the car is not running

The noise then will be a "hiss" or "sissing", it may be an air leak at the booster or the linkage to it and its vacuum hose, or even the hose as well. But that may also induce the engine to rev up because the hose is attached to the intake manifold, and any "external" air leak will make the engine rev up. Check that as well.

  • The noise happens even when the car is not running! I will further investigate – gota Jul 15 '16 at 7:51
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    Car not running: probably air leak...bad vacuum hoses, punched booster diaphragm, worn rubber bushes in booster, take a look to the hose connector from engine to booster, it inserts there into a rubber seat and sometimes it gets loose, just refitting it suffice. If it is too loose you can temporary seal it with high-temp silicone. Tip: get a carburetor cleaner spray, turn the engine on, and spray a bit over suspected areas, the engine will rev up if there is a vacuum leak, because the cleaner is a fuel too. It will help you spot the sucking zone quite fast. – Aram Alvarez Jul 15 '16 at 15:44

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