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The problem began last summer about 2 hours into a ride on rolling hills when I went over a small but sharp bump across road. I have tried to identify and repair problem since then.

I have replaced the head set, had a wheel mechanic check front and rear hubs, but not take apart. I have had a couple of bike mechanics check the bottom bracket. A small bit of roughness can be felt on the right side ceramic BB bearings but mechanics say they should be OK.

I have changed front wheels but noise still happens at speed, usually triggered by a bump; on downhills it usually at speed over 35km/h but has happened at slower speeds once the problem starts on a ride.

I have removed the water bottle holder and the odometer sensor on front left fork and the magnet on wheel spoke but the noise still happens.

This past winter I had what I will call an "MRI" on the bike frame and forks. A problem was identified in the area close to bottom bracket and chain stay where a chain drop damaged the area. This happened in Sept 2019 with a gouge but it's not deep. According to bike mechanics who looked at the damage in 2019 I was advised it should be OK but to cover exposed carbon fibre with paint and or clear coat which I did over 2019-20 winter and I rode the bike in 2020 and the first half of 2021.

I also converted to an 11 speed from a 10 speed and installed a new drive train in 2020. Bike mechanics and a wheel expert said the rear hub on my existing wheel could handle 11 speed cassette. The MRI and repairs were made by the carbon fibre expert this past winter. He warrants his work. I replaced all the cables and housings this spring.

The problem has returned this week on my 4th or 5th ride. The noise starts almost randomly, triggered usually by speed, downhill, and a bump. I have noticed the bolt holding the front brake had become a little loose and wondered if this could be problem as position of brake pads may have moved to one side. Tried again after tightening but noise still happens at speed, usually. It starts whether coasting or pedalling, and stops whether I slow down or not, whether I brake or not, may last longer than 10 seconds or less than a second.

I am pretty sure the noise is in the front of bike but with the way carbon bikes resonate cannot be completely certain. I do not want to replace the bike, not yet, without trying other less expensive solutions first. Any suggestions?

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    I don't think there is an easy answer. Based on the description the sound is caused by road vibration resonating in your frame. If you can find a way to change how the road vibration resonates in your frame you might be able to mitigate the noise. The vibration would likely come from the road transferred to the frame through the hubs. Talk to your carbon fiber expert. He/She might have ideas on how to modify the frame in such a way that the vibration is changed and the sound is mitigated. This would be a trial and error process that could go through several iterations.
    – David D
    Apr 25, 2022 at 13:37
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    What happens to the noise if you lightly drag your brakes? For example, does it stop if you lightly drag your rear brake, but it continues if you lightly drag your front brake? Apr 25, 2022 at 18:15
  • Sounds like you're describing a noise I've had that was loose straight pull spokes on the front wheel. But you've changed that... Hmmmm. I diagnosed/found it by applying light oil around different suspicious areas (obviously avoiding brake rotors/pads) until it went away Nov 11, 2023 at 5:46

2 Answers 2

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I can't diagnose the problem, but we seem to have enough information to narrow it down.

Vibration could be resonance, but with it being accompanied by a loud grinding noise it suggests not. The grinding noise suggests a moving part is faulty OR a moving part is contacting somewhere it's not supposed to.

Since it happens both when pedalling and coasting we can rule out bottom bracket, chain and jockey wheels. And since the front wheel has been changed we can rule out that too.

That seems to leave us with the rear wheel as the most likely option. I'd try a different wheel if possible and if not get the hub stripped down and the bearings checked.

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    Do not have another 11 speed rear wheel but have a very good wheel mechanic who cleans pawels every year or two and neither one of us can feel any roughness in front and rear wheel hubs. Skewers seem very straight and no play in hubs that we can see but wheels also have 50,000 k on them so I will ask Tim to strip down and check hub bearings. Also want him to check head set. Could it be too loose even though I cannot hear any rattle clunk. Could hitting a bump cause vibration and noise resonation in headset? Noise occurred before installation of new head set bearings in 2021.
    – John B
    Apr 26, 2022 at 22:39
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    Can you could borrow a compatible wheel from a friend, even just for a few hours to take it for a ride? I know you and your mechanic inspected it carefully but as pointed out "only happens at 35km/h and even then only sometimes" may be due to a very subtle issue that would be hard to diagnose in the shop. And thanks to your detailed question statement, it looks like the rear wheel is just about the only thing you haven't already tried swapping out. Borrowing an alternate is less work than rebuilding the hub. And a time saver if the problem persists with a borrowed wheel.
    – SSilk
    Nov 10, 2023 at 16:31
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If multiple bike mechanics can't spot the cause with the bike in their hands, its unlikely we're going to be able to do better from your text descriptions, sorry.

Essentially you're going to have to isolate the noise. That may mean swapping parts from another bike, for a test. Or if its frame-related you may have to try adding damping mass to see if there's any particular point which is resonating.

Another thought - can you replicate the issue when riding on rollers ? That may help an assistant identify an area of the bike to look closer at.

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    I don't think I can go fast enough on rollers and noise usually triggered by a jolt from a crack or bump in road. Can't really swap parts although a friend who has an 11 speed rear wheel that I can try. I have thought about a bike mechanic riding bike but it may take 2 or 3 hours before noise is triggered. I start ride with front brake tight to fork but when noise starts I find it loose and right brake pad almost rubbing. Wheel is true despite age. Could the brakes being a little loose start to vibrate at higher speeds causing noise I hear. Not every hard bump makes noise start.
    – John B
    Apr 26, 2022 at 22:48
  • @JohnB this is a hard problem - and will take some sleuthing to figure it out. Start by giving the bike a really good deep clean, makes things easier to see.
    – Criggie
    Apr 26, 2022 at 23:17
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    All parts cleaned before reinstalling to frame after carbon frame repair and repainting. Drive train cleaned. Before last ride seat post and seat bolts, skewers cleaned before tightening all bolts. There are no cracks showing in frame or forks. My wheel expert friend will check, clean rear wheel hub. and check at headset. A cyclist friend will lend me his 11 speed wheel to swap and test if it fits my frame. Although some may feel it is not BB because it happens when coasting and I agree I may still swap out old BB with a new one. Any suggestions on other possible cause to check appreciated.
    – John B
    Apr 28, 2022 at 2:38
  • @JohnB don't assume it is just one problem either - you may be seeing two or more at different times. Definitely a difficult problem, good luck !
    – Criggie
    Apr 28, 2022 at 9:45
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    Yes, it may be more than one problem made more difficult as the noise has been there since Aug 2021. Problem may stem from 2019 when chain was dropped damaging frame behind BB. Switch from 10 speed Sram to 11 speed Shimano 105 in Jan 2020 was before noise started in Aug 2021. Since then headset bearings changed in Sept 2021, noise continued so carbon fibre repair in December 2021. Front brake becoming loose after long rides may be another problem or cause of noise at high speed after bump. Checking rear wheel hub today and addressing front brake repair. Any more ideas on cause is helpful.
    – John B
    Apr 29, 2022 at 10:44

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