Wonder if anyone could help with my weird problem :)
I noticed tonight my car was making a chugging sound, a bit like a train. It wasn't a mechanical sound or a knocking sound. It seems like a woosh or chug chug chug of air and it got faster as i went faster; easier to hear off the throttle too. I'm sure it was at the side of the car and not the engine bay.
My only thoughts are it could be air running past the tyres or air running past the mudflaps or contours of the car.
I also noticed a high tapping sound like stone on stone which gets faster as the wheels turn and wonder if that is a stone trapped in the tread of the tyre - but thought i'd mention it if the 2 were related :s
Any ideas?
re-located into Technical, Make and Model etc would help if only to classify - PU
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The second problem may be a blister in a tyre tread. I had this some years ago.
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What sort of AC is it?
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Sorry it is a new Toyota Auris T180
This is my car (small pic)
toyotaownersclub.com/forums/uploads/photo-20287.jpg
I shall check my tyres for that thanks, i do remember having this clipping stone on stone noise on an old corolla and i am sure i have it on my wifes Rav4 XTR too. :s
AC = Air conditioning??
If so i guess i can only explain it as auto climate dual zone air conditioning and i'm sure the refrigeration unit is at the back of the engine bay (basically right in front of the dash and probably inline with the tyres). That is the best i could describe it.
P.S. I am 80% sure the noise doesnt happen all the time. This is the first time i have noticed it with the window down in 3 months of owning this car.
AC was used to classify otherwise it wouldn't post, now updated - PU
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If it happens with window down at speed it may be resonance.
Any cavity with a small opening with air blown across it (ie like a flute) will cause air to resonate. For musical instruments the frequency is high enough to produce a note. For a car it is probably less than 20 - 10Hz, which means you get a "chugging" effect in the car.
If this is the cause, opening window further or closing it may effect the sound as will driving with wind behind you or into the wind. However this effect is normally only noticeable at higher speeds (over 40mph maybe) or on windy days.
If it was something to do with air conditioning or engine, it would make the sounds at low speeds (less than 30mph) and maybe high revs.
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If it happens with window down
Indeed. Another way to deal with this is to open another window slightly - this prevents the air within the car acting as the acoustic equivalent of a spring, and prevents the buildup of the pressure fluctuations.
For those interested in the theory - the car becomes a Helmholtz resonator, and, as Saltrampen says the frequency is low - this is because there is a large volume of air in the car, and so, the equivalent spring is very compliant - opening another window makes the spring infinitely compliant, and therefore makes the resonant frequency zero, and hence gets rid of the oscillation.
Number_Cruncher
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I get a rhythmic resonance with my sun roof open at certain speeds. Closing it up an inch or two usually stops it.
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Old Skool
Check the wheelnuts.
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