Question:

Why do delivery trucks make a 'pssst' noise when parked and unattended?

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Why do delivery trucks make a 'pssst' noise when parked and unattended? I thought it only occurs during driving and stopping.

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  1. they want your attention to tell you a secret....(LOL)

    Alot of the newer trucks have an air-ride suspension and when parked,,, they will leak themselves out thus creating the sound you hear....


  2. Air brake relief valve releasing pressure from tank..

  3. The air for the "air brakes" is releasing some built up pressure

  4. The psssst' noise is air compression!

  5. Its the purge valve located on the air drier releasing pressure. When it does this, it also vents moisture. Its a normal function of any air brake system, from semi's to trains.

  6. It's the pressure valve on the air storage tank venting.
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