Buzzing/humming sound when accelerator in high speeds?

Discussion in 'Freightliner Forum' started by John Trollenski, May 19, 2022.

  1. John Trollenski

    John Trollenski Bobtail Member

    Nov 4, 2015
    Hello, my truck is a manual 2018 freightliner cascadia evolution with a DD15 engine. Recently, my truck started making a buzzing/humming-like noise when I’m accelerating at 45mph and beyond, and it gets louder the faster the truck is driven. However, when the accelerator is let off, the sound disappears. After doing some online search and whatnot, I thought it would be the turbo since it has never been changed and the truck is now at 573,000 miles. But when that was changed, the sound didn’t go away. The truck was pulling fine prior to the turbo change, and it still is now, but I thought it would’ve been that.

    I have recorded and linked a video where you can hear the sound. It has only been making this sound and luckily nothing else has been affected(so far).

    Any thoughts as to what the culprit would be?

    Thank you!
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  3. Tigerfishinc

    Tigerfishinc Light Load Member

    May 28, 2021
    Check the bearing grease point for the clutch
  4. RocketyMan

    RocketyMan Medium Load Member

    Jun 5, 2015
    You can totally tell it's drivetrain related.

    You told us the engine. DD15...great. Now what about the transmission? Is it automated....manual...etc...?

    I'll give you a few hints on what that "noise" might be, or rather not be. For's not going to be the turbo. Turbos spin---FAST. If you did better research on your turbo inquiry, then you would need to distinguish what type of turbo you have. Do you have a turbo compound? [Or] Do you have a Asymmetric Turbo? Both of those have characteristic sounds related to them. I'll guess you have an AT.

    For one, it wouldn't be your clutch throw-out bearing (if you have a manual transmission or Eaton US+)--although, you DO need to make sure this is lubricated periodically. How can you tell? The sound varies with ROAD speed. Your hydraulic clutch would put constant pressure on the throw-out bearing. Also...the sounds only happens with engine-load. You can hear the sound almost be driven by coasting, too.

    Next thing for you to do...can you get the same sound to happen with a different gear at the same speed? What gear were you in at the time? 9th? Do you have a direct drive or overdrive transmission? 10 spd? 12 spd? 13 spd? etc...

    Think like like a master-tech...not a lube-tech.

    P.S. good reference to the video btw!
    QUALITYTRUCK Thanks this.
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