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I recently noticed my car is making a barely-perceptible, low-pitched, buzzing or droning sound at highway speeds. It kind-of sounds like some cars' exhaust, but it's quiet enough that I seem to be the only one in my family who is hearing it. (It's about on the same volume level as natural "road noise".)

The sound only begins to be noticeable around 45 MPH. Once the car is going fast enough that I can hear it, the sound does not go away until the car has slowed to below the same threshold.

The sound does not follow, nor does it seem at all affected by, the engine's speed. (I've listened during normal usage as gears shift automatically, and also forced up/down shifts and shifted to neutral - none of these cause any change to the noise's pitch or volume.) It also is not uniquely affected by braking - so long as the car continues to travel faster than about 45 MPH, it remains present and at its usual pitch and volume regardless of whether or not the brakes are applied.

I've tried to localize the sound to no avail. It feels a little like it's coming from the front of the car, but the other day I could swear it seemed to be coming a little more from the rear. Since it only happens at 45+ MPH, and is fairly quiet to begin with, listening from outside the car is not an option and it gets drowned out by the wind when the windows are down.

The sound only seems to be slightly affected by vehicle speed. It just barely raises or lowers pitch as the car goes faster or slower, but the volume does not seem to change much.

The car in question:

2012 Dodge Avenger SXT
2.4 L inline-4 DOHC engine
6-speed automatic transmission, FWD

Brief recap of sound characteristics:

  • Low pitch, low volume. (Barely noticeable against road noise.)
  • Occurs while vehicle speed is >= approx. 45 MPH.
  • Unaffected by engine speed, gear selection, or braking.
  • Pitch has a slight direct relation to vehicle speed.

Given that the sound seems to be somewhat related to vehicle speed, but independent of engine speed, one of my first suspects was the wheels or tires. However, the tires appear to be in good shape and (recent weather fluctuations aside) don't seem to have problems holding air.

What are likely causes of this type of sound that I should be looking at?

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    Stab in the dark: Wheel bearing?
    – Zaid
    Oct 21, 2015 at 19:54
  • @Zaid - That's what I was thinking too ... To the OP: have you hit any curbs or potholes recently?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 21, 2015 at 20:37
  • @Paulster2 It's a possibility. I don't recall any events substantial enough that I'd expect damage, but I'm also not the only user of the car.
    – Iszi
    Oct 21, 2015 at 21:31
  • @Zaid and Paulster2 - Is there a "driveway test" I can do to check the wheel bearings?
    – Iszi
    Oct 21, 2015 at 21:37
  • Just had the oil changed and asked the mechanic to check for the sound. He said wheel bearings are fine. He listened for it with the car running in the air and said it seems to be coming from the transmission differential.
    – Iszi
    Oct 28, 2015 at 15:05

2 Answers 2

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jack the wheels up one by one and spin them by hand. if it makes (sometimes somewhat quiet) metal grating noise the bearing(s) needs to be replaced.

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I've had cars that had a hole in the centre exhaust that only created a soft 'booming' noise at certain engine revs (harmonic resonance issue?). The noise must have been coming / going at certain revs (1300 odd revs in a low revving beast of a straight 6), but I only heard it at speed because that was the only time the car was cruising at such low revs.

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  • This is not what I'm experiencing. Note that the question specifically states the noise is independent of engine speed - as long as the vehicle speed is above a certain point, the sound remains present and its pitch and volume are not affected when the engine speed changes independent of vehicle speed (e.g.: down-shifting while maintaining 60 MPH).
    – Iszi
    Oct 23, 2015 at 14:53

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