Weird car noise
January 6, 2012 7:31 AM   Subscribe

What is this sound my car is making? (Link to file below the fold)

I tried to record it while driving since describing in words is difficult (mp3, sorry, you'll need a popup blocker!): Mediafire

At lower speeds like the 30s (mph), the noise increases in volume and gets faster when accelerating. I think. Then at higher speeds (50+ mph), the sound appears when I release the gas pedal to slow down; this recording was made at highway speeds, somewhere around 60 mph I think. It's like a...clunky flutter. It's hard to remember details like that while I'm paying attention to actually driving, though.

I'll be looking for a trustworthy mechanic eventually, but I'm hoping for some ideas so I won't get caught too unawares (not a car person). Thanks in advance.
posted by Ky to Travel & Transportation (6 answers total)
Best answer: Probably a severe alignment or tire wear issue. I would check all the tires for strange wear, make sure all your lug nuts are present and tight, and if it's none of those, take it to an alignment shop and have them take a look at it.
posted by cosmicbandito at 8:01 AM on January 6, 2012


Is there any other evidence? Vibration? Either through your hands or through the wheel? Is it more apparent on any particular kind of surface (ie does driving over road irregularities start or stop it?).

Not enough info for a diagnosis here, but this could be anything from a worn suspension bush, something flapping under the bonnet against the chassis or similar. if it is louder at 30mph than 60 it is more likely to be a suspension component and hence worthy of sooner attention.

It seems to get louder as you slow down (although engine noise is hard to determine in that clip) so I am leaning towards a control arm bush or similar. It sounds like the cause is too weighty to be something banal, but it is REALLY hard to be certain. This could be pretty serious so needs to be looked at sooner rather than later.

It sounds like metal on the body of the car so it is almost certainly not tyre noise or caused by alignment. It's totally the wrong kind of noise. This is something solid vibrating against something solid (most likely the chassis/body). The fact that it is of such a low pitch suggests something weighty, which means something important!

Sorry to be so vague, but I can't be confident about it enough to say 'don't worry about it' which means... um... worry about it, I guess. Go and see a mechanic at your earliest convenience.
posted by Brockles at 8:06 AM on January 6, 2012

You've done a bit of correlation but I believe the thing to do first is determine whether this wub-wub-wub noise varies in frequency with -engine- speed, -road- speed (mph), whether you're driving straight or around a curve, whether stronger accelerating, "floating" or using engine braking to decelerate, or no variation can be correlated with anything. I don't hear any frequency variations in the clip. The reason you do such a correlation is this: noises that vary with road speed are generally -after- the transmission (where the speed of drive shafts and the like run at the rotational speed of the wheels); noises that vary with engine speed are before, or perhaps within, the transmission and might be isolated to the engine or its mounts; noises that vary on curves point to differential problems; noises that happen over bumps are usually in the suspension pieces; really random noises are exceedingly rare. You can also try seeing if the car makes the same noise when it's in neutral, or a different gear. For example, you may be driving in 'D' or top gear. Downshift a gear and see if the noise changes. If you hear the noise when the car is coasting, put it briefly in neutral and see if the noise goes away.

It's often helpful to jog people's memory by stating make and model of car, too; this sounds a lot like my 1965 Plymouth Valiant did when it had a bad drive shaft U-joint bearing. That noise, BTW, varied with road speed, was stronger on acceleration than on over-run, didn't happen when the car was not moving and in neutral, didn't care which gear I was in, was there but diminished when moving at road speed with the transmission in neutral.
posted by jet_silver at 8:31 AM on January 6, 2012

Response by poster: Hmm, okay. To answer some comments--

This is an old Saturn SL2 from 1997. The noise didn't appear when parked or stopped at a light. I always have to drive over a bunch of speed bumps in my parking lot to get anywhere, so perhaps I went over one too fast some time ago, but the noise doesn't start/stop depending on those now, nor does it matter if going straight (e.g. on a highway) or making a turn (e.g. stop light).

I'll see if I can observe more closely to the noise's dis/appearance, but I'll look for a good mechanic ASAP. Thanks so far!
posted by Ky at 9:37 AM on January 6, 2012

Almost sounds like a worn strut or strut top bearing.
posted by narcoleptic at 10:18 AM on January 6, 2012

Response by poster: Final update: When the mechanic took my car for a test drive, they said it sounded like a bearing issue and would take a look for a quote.

It turned out to be much simpler--that sound (which is sort of a straining-rubbing 'wub wub' at lower speeds and more of a knocking sound at higher) was due to the front driver-side tire missing a lug nut and the other lug nuts being loose. The mechanic was perplexed how this could be, since you have to remove the cap to get to the lug nuts, so this must have happened in a previous tire rotation. Turns out cosmicbandito was right on one of the points.

The fix was fast and free. Thanks to everyone for the input!
posted by Ky at 10:26 AM on January 11, 2012

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