Resonant Hum At Speed On Some Roads

[mpg_junkie]

Hi all,

Looking for some help. I have a 2012 yaris which in the last month developed a resonant hum at speed on some roads. I assumed it was tyre issues as when I kick the tyres (rears only) they give out the same noise I hear when driving (ringy pneumatic noise like an overinflated ball bouncing on concrete) so I changed all the tyres to a different brand and model renowned for low road noise (Michelin energy saver +), but the ringy noise is still there.

So, is it likely to be the alloys, brake drums, etc. I get the same noise on each side at the rear. Car has 32000 miles and well looked after. Any opinions welcome

Thanks.

[CPN]

I assume you've checked that the pressures are at the recommended levels? (and not over inflated - which is how they sound...)

[ToyotaAuris]

Have you ever carried any large items in the car? If so the bearings may have gone.

[mpg_junkie]

Hi, tyre pressures are as per manufacturer's spec (also played about with them with no effect) and no heavy loads ever carried. Starting to think it might be suspension or something resonating?

[eyemdee]

Worth a try tapping around the exhaust where you can reach it. Could be resonance from the cat or a damaged bracket somewhere?

[mpg_junkie]

Ok, tried tapping various parts on the rear of the car. The tyres give out a ringing sound at the frequency of the noise I am hearing while driving (240hz) and this can be heard when tapping the rear trailing arms but no where else. Seems like the rear of the car is resonating, it only started a week after I bought the car, starting to regret buying a toyota :(

[CPN]

When you say "resonant hum at speed on some roads", what speed are we talking here?

I've just been out and had a knock around the rear of my Yaris Hybrid with a rubber mallet and yes, there is a sort of "ringing" sound when you tap the tyre sidewalls and a similar sound when you hit the lower trailing suspension arms but none of this, at least in our car, translates into a "resonant hum at speed on some roads"... I would also say that this kind of sound from these places is probably just as a result of the springs being under tension and that is the source of the "noise" when tapping... This may be a red herring and the source of your noise could be something completely different...

[mpg_junkie]

It starts at any speed over 25 mph up to 70+ and stays the same frequency. Loudness changes with road surface and often disappears. I thought for sure it was tyres but I changed from old dunlop to new Michelin and it is exactly the same tone. The tone I hear when driving is the same tone when I hit the tyres, so I assume the tyres are sending this sound through the chassis into the car.

[CPN]

You used the phrase "Loudness changes with road surface and often disappears". Is this over the same route every day? By "disappears" do you mean completely or just drops in volume? Is the disappearance abrupt? Is it coincident with a change in road surface?

(by the way, never "assume" because, as the old saying goes... "it makes an ass of you and me!" ;) )

[mpg_junkie]

Hi CPN,

it is loud about 30-40% of the time (not very loud but can be heard over in-car chat), audible if you listen 50% and disappears maybe 10-20%. I travel various roads and I think it is more noticeable over some road surfaces than others but not with a direct correlation of smooth road = no noise, rough road = noise type of thing. Rarely the change in/disappearance of noise is abrupt, normally it just gets less.

Just a note, listening this morning the resonant noise also fluctuates (a bit like Dr Who's Tardis appearing but not that modulated).

Philip

[CPN]

From that, the only thing I can think of is suspension bushes that have hardened in some way so that they are not doing what they are partly supposed to do and that is to help insulate and dampen road/tyre noise from getting to the passenger compartment. Perhaps one has got gummed up with tar and/or grit somehow? Clutching at straws now really but getting it up on a lift and having a very close inspection of all of the suspension mounting points and moving pivots would be my next avenue of approach...

[dcweather]

Well I got something like this on my Skoda Octavia and now in my wife's Yaris, but much less so in my Seat Leon. I have dedided that it is just certain types of coubik tar mac and a lot of cars do it but once you've tuned your ears into it you get obsessed with it. My wife for example doesn't hear it.

[Neil robertsin]

When the noise occurs lightly apply the hand brake, if the noise changes or disappears it would indicate the rear wheel bearings, although your car hasn't done enough miles for them to be worn potholes speed, humps,kerbing etc can damage them.

[mpg_junkie]

Checked out the hand brake thing and this has no effect. I am starting to think it is an odd resonance due to the combination of the tyres, alloys (stock toyota) and trailing arms/suspension. It happens on most roads and is more noticeable when I am in the car alone as having a heavy passenger reduces the noise slot (affects suspension and thus resonance???). The dealer suggested it is just road noise but in my 23 years of driving a multitude of cars I have never experienced this type of hollow resonant low frequency pinging noise; if this is typical toyota road noise then someone at toyota needs publicly flogged while being made to listen to this noise.

I have also noticed that changing the tyre pressure roughly affects the speed at which the hollow resonant hum occurs, with lower psi causing lower speed prominence of the noise and higher psi causing higher speed prominence, although the noise still happens at all speeds over about 15 mph the pressure causes the speed of noise loudness to shift. In all of this the tone/frequency of the noise remains constant at various pressures and speeds.

Still baffled though, as is the dealer looking in to it.

P

[Catlover]

Have you changed any of your tyres? (sorry if this has been mentioned before, not had time to look at the whole thread)

[mpg_junkie]

Hi catlover,

The car came with 2 brand new Michelin energy saver plus tyres on the front and 2 half worn Dunlop fast response tyres on the rear. After about 3 weeks of ownership the hollow resonant sound just appeared. I got the worn rears replaced to 2 Michelin energy saver plus tyres as it sounded like the noise was coming from the rear, however the new tyres made no difference. I have also had the front and rear suspension, springs, bearings, etc inspected by the dealership I bought the car off and they said everything looks sound.

Anybody else using Michelin energy saver plus tyres (or any Michelins) on their yaris? (2011 onwards).

[MikeSh]

If it's resonance it could be a failing damper. Might not show on a visual inspection. Hard to check without changing them out though.

Hard to track down some of these suspension sounds. My Ford has an odd clunk on some bumps, but despite changing quite a lot of the suspension parts (for upgrade, not specifically the noise) and 'checking' what's left we still don't know what's doing it

[Neil robertsin]

You're probably getting quite desperate by now so here's a couple of straws to grasp,I've heard of two instances of noise/vibration being cured by loosening and retightening fasteners one was the exhaust heat shield on a BMW bike that 'groaned' when hot, loosening and retightening when hot cured it.The other was a Kawasaki on which engine vibration was reduced by loosening and retightening the engine mounting bolts once the bike had done a few thousand miles ,I'm wondering if the same trick might work on you're rear suspension. I've just had a good bang around my rear suspension and the only thing I could get to make a noise were the springs themselves perhaps spraying lube on them where they contact the spring seats may be enough to change the harmonics.

[Catlover]

Turn the radio up ?

[fastbob72]

Have you checked your engine/transmission to subframe/chassis mounts at all.

The harmonic dampener came off my rear trans to crossmember mounting and not only led to some horrendous noise/vibration when driving as it wedged itself between the bellhousing and subframe even with it removed there is still a resonance/hum/low vibration that persists.

It just goes to show that it clearly was put there for a reason and I haven't had a chance to fix it yet making the car a lot less enjoyable to drive :(