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03-21-2012, 11:49 AM | #1 |
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Strange Resonance at constant 72-73mph
I have a 2012 6mt Competition Pack E92, which has developed a strange "wowowow" resonance which can be heard -especially on smooth surfaces- at a constant 72-73mph, but only in 6th gear. The same engine speed in 5th, or the same roadspeed in 5th does not cause the sound.
If you close the throttle, the noise goes away. OK - you could say drive faster or slower and no problem, but there are many speed cameras on some sections of my journey to work and I really do not want to take even longer to get there! The car has 4500 miles on the clock, and Pilot Sport 2 tyres. Dealer has tested the car and agrees that the noise is there, has changed the gearbox oil and sent a query to BMW tech support. The tech who came out with me in the car thinks it is an engine fuelling issue, but I am not so sure. I would have thought it would be a gearbox issue. Has anyone else come across this? TIA Tony B |
03-21-2012, 05:12 PM | #2 |
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I have had resonance but it's from my tyres and only happens on certain road surfaces, especially smooth ones. Tyre resonance is characteristic of low profile tyres.
Yours sounds more like transmission given that it only happens in 6th and is independent of engine speed. It sounds unlikely to be coming from the wheel bearings, diff or prop/axle shafts given that noise from these components would be occurring regardless of which gear you are in. If you ever need an extra pair of ears, I'll be willing to help. I don't live too far from you (seen you on m3torque). |
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03-21-2012, 11:19 PM | #4 |
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Sorta sounds like tires but then why not get the sound at that same speed in another gear? OP says no resonance in other gears? And why would it immediately go away with a closed throttle. That part does not sound like tires.
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03-22-2012, 01:38 AM | #5 |
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The surface makes a difference only in that coarser surfaces generate enough noise to drown out the resonance. It is still there if I really listen for it but I dont notice it enough for it to be annoying.
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04-23-2012, 02:27 PM | #6 |
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Update
Well, my car has now been in the dealership twice, as they attempt to fix this.
1st Visit - gearbox oil change, engine management software updated. Result - absolutely no difference. 2nd Visit - transmission mounting bolts slackened off, exhaust bolts and mountings slackened off, then everything re-tightened from the front to the back. Result - the resonance can now be heard over a slightly wider speed range, now being noticeable from ca 73 - 79mph. I have also spoken with a BMW tech in Germany, who has little doubt that this is a gearbox issue. The bolt slackening/tightening has merely changed the acoustics of the sound transmission path. I will be speaking with the dealer again tomorrow and be pushing for proper remedial action (=new gearbox) as the typical unofficial UK cruising speed (70-80mph) is now a very annoying zone. |
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04-23-2012, 02:34 PM | #7 | |
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04-23-2012, 02:51 PM | #8 |
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04-23-2012, 03:01 PM | #9 |
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Could be exhuast sound and tire/road noise getting close to the same frequency. This can cause a "beating" sound when the frequencies are close but not exactly matched.
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04-23-2012, 06:42 PM | #12 |
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04-23-2012, 10:05 PM | #14 | |
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If you can remember, my iPhone picked up that high pitched whine at motorway speeds. |
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04-24-2012, 04:03 AM | #15 |
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04-24-2012, 06:49 AM | #16 |
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haha, I had that on my 535. The dealership acknowledged the noise, but blamed it on the tires (Bridgestone). There was nothing they could do and I had to accept this. Every time I switched to winter tires, the noise went away. It would constantly drone between 130km/h and 140km/h. They called it "tire feathering"
Good luck, keep us posted. |
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04-24-2012, 10:52 AM | #17 |
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I had a horrible drone/noise on one stretch of Hwy 231 here in Southern Alabama with my Z06. Couldn't reproduce it anywhere else, ONLY on a certain stretch of this road. I thought my gearbox was going out because I JUST changed the tranny fluid and thought I did something wrong. It was the tires not liking the road, because it never did it on any other road.
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04-25-2012, 05:36 AM | #19 | |
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I will attempt to record it in the next few days, but as we have lots of very wet/windy weather here currently (that'll be the global warming carp of course) it is less noticeable. |
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04-25-2012, 05:41 AM | #20 |
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Good idea.
I was thinking about putting my winter wheels/tyres on to experiment. Carp weather is a bit of a disincentive to lots of outdoor jack/wheel-brace time though, at the moment. The joys of a UK Spring. Not |
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05-05-2012, 08:38 AM | #21 |
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I have this problem on my car as well!
I'm driving a 2011 E92 DCT and have this resonance in 7th gear between 1,500-3,000rpm. It does not happen all the time and can sometimes be quite soft and sometimes really loud. Occurs on all sorts of roads, so I doubt that it's a tyre issue. Car drives well and shifts well too. Took the car in to the M dealership here for some seat of the pants diagnosis with a couple of the sales guys here. We went for a quick trip and they concluded they've not heard this sound before but stopped short of saying it's not normal. I guess you can conclude that it isn't normal if they haven't heard it before right? Other M drivers feel it could be an exhaust backpressure issue or a leaky exhaust, but also acknowledged this was not a sound they've heard before. What pisses me off is the CSA (the guy who attends to customers bringing the cars in for servicing, etc) told me this is an exhaust backpressure issue and is normal. He kept repeating it was normal and it's like he was saying it's normal so I would stop questioning him. How the hell can a droning resonance be normal?!?! On a $400k car?? You're kidding me right??? I have no idea what the cause of it could be but am worried it could be bad running in procedures as the guy who arranges the tints and other pre-delivery stuff put 140km on the odo saying the tint people could not come to the shop, had to do this, had to do that. In tiny Singapore at rush hour on the expressway might not be the best way to run in the car for 140km, as well as I do not know how he has driven the car, not to mention that 140km on an island that measures some 30 odd km from east to west is much more than necessary. When I told the CSA this, he checked the system and said that it showed PDI service only clocked 20km, but the PDI fella and some of the sales people know about the 140km on the odo and have fessed up to it. Covering stuff up gives a person more reason for suspicion no? That pisses me off even more! Have to say that the sales people try their best to help and have been honest with me as far as I can tell. Car goes in for 5 days on Monday and I hope the first M dealership in the world can make good and hopefully rectify the issue. Brand new car with 2400kms on it and already facing issues...sigh...will keep you guys updated on what our M dealership has to say about this. |
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05-06-2012, 01:06 PM | #22 |
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@sg-m
I doubt that yours is the same issue as 1500-3000rpm is (a) starting much lower down the rev range and (b) over a broader range of revs. The car has been in to the dealers 3 times for this now (a total of 7 days in all) and I am beginning to lose patience. I asked the SA to raise this with BMW GB as I am not happy. This has been done, and I am now advised that BMW GB have escalated it to BMW M. I am going to give them a few days to respond, and then the next step (in my opinion) is a proper vibration signal analysis job, using the right diagnostic equipment. I used to work for a company that specialised in testing gearboxes, using the vibration signature to detect hidden faults. They could trace faults down to gear or bearing level without ever opening the box (their target market was remote, inaccessible equipment). It does not have to be done by ear, or by dismantling the transmission. It has to be done, though! |
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