I bought a Mazda 3 as my "to work and back" hack car back in May. Immediately it became apparent that at 55 MPH a strange resonance noise could be heard - a whoop (thrum) noise that sounds for a second and then is silent for about 2 seconds. It can be heard until I get to about 68 at which point it seems to vanish. I don't recall hearing the noise when I tested the car but I was on 50 MPH limit roads and it was wet which masks the sound somewhat. Sadly 75% of my daily journey is on 60 MPH limit roads where I find myself doing the speeds that triggers this.
I assumed it was the rubbish tyres so in July I changed the two rear tyres - one an old tyre (can't remember what) and the other a new Sunray Chinese ditch finder. Car was quieter but noise remained. I swapped the new rears to the front and moved the fronts (two Wanli tyres with lots of tread left) to the back. It was difficult to tell if the noise moved with the tyres but the rear became louder - the new tyres were 68 dB rated. Wanli are rubbish tyres so today I swapped those - noise remains although the car is much quieter and the ride is much better in other respects as a result which makes troubleshooting a tad easier.
The noise sounds between 55 and 68(ish) vanishing at 70. At 55-65 the noise remains fairly constant in pitch and occurrence. It returns at about 78 but the 2 second gap between "whoops" goes and it becomes almost a constant noise. The car has no shakes or vibrations through the steering wheel or seats and if I put the car in neutral and coast down a hill the car doesn't loose speed while if I release the steering wheel it continues going where it was pointed.
Under the engine is a plastic shield that was loose and this evening I have tightened that up - no difference. There is no noise when going around roundabouts on different lock, no ticking or similar on full lock.
Any thoughts on what next? I am out of ideas.
Thank you.
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To get that sort of beat signal, you're looking for something that is synchronized with wheel rotation.
If the sound persists if you dip the clutch and allow the engine to idle, then, I would begin with the wheel bearings and brakes. Front wheel bearings may best be listened to with a stethoscope on a wheel free ramp, or alternatively use a thermometer to highlight any differences in bearing running temperature. If the rear wheel bearings are taper roller, then they can be inspected (other than the inner race), but are probably cheap enough just to replace on-spec.
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N-C's probably on the money, but i've been finding modern mass market cars, particularly hatches and estates, to suffer from severe road noise especially from the rear...combination of usual cost savings and the trend to elastic band tyres the missing soundproofing increasingly shows itself.
it would cost peanuts to do but if you remove the plastic or thin carpet type covering from the rear wheel arches/panel a pound to a penny you find no soundproofing whatsoever there, temporarily lining some spare carpet underlay there and the surrounding boot and under rear seat areas for a few days might well surprise you with a new found refinement, if successful then proper self adhesive pads can be bought cheaply from ebay to make a good permanent job.
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Being an amateur I can't argue too much but I would expect a wheel bearing to have a more consistent noise that doesn't vanish at a higher speed? I would also have thought I would experience some sort of drag on the car - pulling it to one side, particularly at speed?
I have tried some make shift insulation! We had a huge disk array delivered (IT stuff) and it came with a load of thick packing foam shaped like egg cartons that now sit in the boot. It has made things road noise quieter but not this sound...!
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The wheel bearing itself would make a consistent noise, but, the beat signal you describe, with the vibration pulsing is usually cause by two nearly consistent sources of vibration adding together.
By the time a noisy wheel bearing is causing enough drag to be felt, it's completely ruined, and you'll only get another mile or two before it locks up solid. However, it takes only a tiny imperfection on a roller or a race to make a bearing begin to make noise, and the noisy bearing can remain in-service for a considerable period of time before the noise gets worse.
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>> and the noisy bearing can remain in-service for a
>> considerable period of time before the noise gets worse.
I'm glad that you mentioned that NC, because I have a slight wheel bearing noise on my Forester, around 60-65mph. It's hard to pinpoint, but sounds like nearside front, but I'll leave it until it gets worse. The only worry is that I've heard that they can wreck the entire hub if left for too long, but I would imagine that they would have to be pretty loud by the time that happens.
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>>but I'll leave it until it gets worse.
Yes, now you're aware of it, it's the sort of job to get done at your convenience, rather than waiting for the catastrophic failure at the end.
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Thanks for the info. Makes me wonder how shot the bearing was on the 3 year old RAV4 I bought and then drove the next day to Holland... I told them when I test drove it that it was bad and I could feel that drag!
I have the car booked for a check this afternoon so will update.
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I've seen many wheelbearings which make noise but, even with the wheel jacked up and free to rotate, you can't feel any problem, and it's only when you get the disc or drum off and you can feel the bare hub rotating on its own that the bearing failure becomes obvious, and some wheel bearings even then can feel OK, but it's only when you get them apart and look at the balls/rollers and races that you see the fault.
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On a longish boring journey, I played with the noise of a grumbling front wheel bearing on a T5 Transporter. I could change pitch and volume of the noise by varying speed, left or right pressure on the steering wheel, positioning relative to the camber of the road, or a combination of any.
Never quite got it to play a tune.
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It has been confirmed as OSF wheel bearing so is booked in for a weeks time to be fixed. A friend has the punch tool but I have never done the job or seen it done so would rather just pay someone...
Thanks for all the advice.
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Mazda Mazda 3 - 04 2.0 Resonance noise at different speeds - Number_Cruncher
