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Thread: Droning Rumbling Vibration / Hum

  1. #1
    Join Date
    May 2018
    Location
    Wyoming, USA
    Posts
    4
    My Cars
    2006 BMW 330xi

    Droning Rumbling Vibration / Hum

    2006 330xi automatic tranny 145,000 miles.

    Startedhumming about 10k miles ago, barely noticeable at first, but slowly and consistently getting louder. It doesn't make the sound when at a standstill. While driving, it's a persistent, always-there vibration / rumble / droning noise, which changes only pitch with change in speed.

    It is a very low pitched rumbling drone 10-25 mph, at 25-35 mph its sort of a whu-whu-whu-whu vibration, and at higher speeds it sort of sounds like my motor is just loud. Highway speeds it's a pulsating hum you can feel through the whole vehicle, but not a crazy vibration that shakes things around. It does barely make things like the headrests wobble a tiny bit at the same frequency as the vibration when at highway speeds. It changes pitch, not volume, only with an increase in wheel speed.

    The sound's source is the rear passenger side of the vehicle. It is completely speed dependent, not drive-train load or steering/cornering dependent, and the vibration doesn't change pitch OR volume with shifting into neutral at ANY speed.

    Here's the troubleshooting I've done thus far:

    Since it's a consistent sound coming from the rear end, no clunk /clang shifting into drive or reverse, with no change in volume while accelerating, braking, cornering, or putting it in neutral going down the road, I'm ruling out the driveline, carrier bearing, flex disc, front wheel bearings, and/or sticky calipers.

    Changed the rear passenger wheel bearing. (twice - put it in backwards the first time. Seals on both sides were black/dark grey with no markings to indicate installation direction)

    Lifted the car in the air and put in drive, going slowly from 0-60mph and and back, and it makes the EXACT same sound as when it's on the road. Tires were on the car. Going to do this again, but with wheels removed.

    When lifted, the differential makes a clicking sound when I turn the rear wheels/axles by hand, so I was thinking this may be the cause. However, I've just learned that this clicking may be normal. Also, it's not a whining or high pitched metallic sound, but more of a rumble or pulsation, so I'm thinking it's not the differential. Diff is full of fluid, looks clean.

    Is it too early to rule out supports, bushings, and mounts since noise is there while in drive / wheels not touching the ground?

    Thanks in advance for your insights!
    Last edited by yousir; 07-10-2018 at 02:13 PM. Reason: added notes about diff...

  2. #2
    Join Date
    May 2018
    Location
    Wyoming, USA
    Posts
    4
    My Cars
    2006 BMW 330xi
    I lifted the car again, drove 0-60mph with the wheels off - same noise. Removed half axle from differential on driver side and noise is still there, only more of a grating, metallic sound than before.

    Passenger side axle wasn't spinning. This could only be the differential, right?

    Here's a video with the sound. https://www.youtube.com/watch?v=nyzIX_0vfNw

  3. #3
    Join Date
    Jan 2016
    Location
    Ca
    Posts
    6,981
    My Cars
    2001 525it
    Drain the fluid look for metal particles in the oil

  4. #4
    Join Date
    May 2018
    Location
    Wyoming, USA
    Posts
    4
    My Cars
    2006 BMW 330xi
    Thanks jclausen. I've drained the fluid and no signs of particles.

    I noticed that while the noise coming from the differential is quite loud, it is different when the axle is removed. It's no longer a rhythmic droning sound, just a metallic whirring.

    I also noticed that the right cv boots are new looking and the left aren't, and the left axle moves pretty roughly back and forth, while the right is smooth. I'm going to replace the right axle and give an update.

  5. #5
    Join Date
    Dec 2007
    Location
    Lincoln,CA
    Posts
    72
    My Cars
    2016 M235i
    I just had a similar issue on my '07 328xi and had to replace the front differential=noise gone! The front drive shaft joint also were bad.
    BMW FANMAN!

  6. #6
    Join Date
    May 2018
    Location
    Wyoming, USA
    Posts
    4
    My Cars
    2006 BMW 330xi
    I replaced my left rear wheel bearing, and now most of the noise is gone. I also inspected the current left drive axle off of the vehicle, and one of the CV joints is definitely shot. I have the new axle now, but a different problem - steering wheel lock malfunction, my car won't start for me to move it to the garage. Waiting on a coding cable and steering lock emulator... I sure do love this car!

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