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I recently purchased a brand new Scott Genius 950 at a local bike store. After bedding in the brakes, I noticed a rattling noise while riding coming from the front disc brake. I brought it back to the bike shop, they disassembled the front brake and put it back together, but the noise is still there.

I was told to bring the bike back when the head mechanic is in, but I thought it would be worth posting a video of the noise here. It seems to act up the most when I turn sharply left or right. It doesn't always rattle, and it does it when I am not braking.

Maybe it isn't the brake, but the spokes? I am not really sure.

YouTube Video:

Any suggestions?

UPDATE 1

I just got back from the shop, the head mechanic took the front brake apart and put it back together. I rode it around the parking lot for a while, and just now around the neighborhood. Seems that the noise is gone (for now!).

I asked what he did, but I don't remember all of the technical details. Definitely re-aligned everything, tightened everything, mentioned something about [retracting?] the spring, etc. I wish I remembered more of what he said so I could share it here.

UPDATE 2

I just got back from a test ride around the neighborhood. I can still get a slight rattle out of it when dropping the front end after doing a wheelie. Since the front brake has been rebuilt by the shop mechanic, I am not too worried about safety. From the feel of it, nothing is loose, and I have full stopping power. I suppose I will just have to learn about it on my own, and continue to investigate.

UPDATE 3

So, I am able to reproduce the noise (only for a fraction of a second) when dropping the front end down, hitting a curb at an angle, and turning sharply. It makes a very quick, very quiet ching noise. From this, I am now thinking that it may be from the flexibility of the fork causing the rotor to make brief contact with the pads. After learning how the disc brakes on my bike really work, I am not concerned that this will be a safety issue, and may wear in with time if my conjecture is correct.

I found some interesting information after looking at the dealer's manual for my brakes: SHIMANO Hydraulic Disc Brake 4-Piston Caliper Model: BR-MT420

https://si.shimano.com/pdfs/dm/DM-MBBR001-04-ENG.pdf

On Page 8 about a third of the way down the page it reads "The 203 mm and 180 mm disc brake rotors have a larger diameter than the 160 mm disc brake rotor for cross-country bicycles, and so the flexing of these disc brake rotors is greater. As a result, they will interfere with the brake pads.".

Very interesting, as those are the exact size of the rotors on my bike. So maybe this is normal and expected?

Thank you to everyone who has responded, and if anyone has any further ideas or experience with this issue, please reply :)

  • from that sound, I would hazzard a guess at something touching the rotor. Any change in noise when applying the front brake? Can you see anything obviously touching the rotor? Does it still make the same noise when you lift the wheel off the road surface and spin? – Henry Jun 15 at 19:16
  • Hi Henry, thanks for your comment. When applying the front brake the noise stops. No, I cannot see anything touching the rotor. If I lift the wheel off the surface and spin, I cannot reproduce the noise. – Carman Cater Jun 15 at 19:24
  • I would look and check to see if the pads have been installed correctly. At a guess, and this really is a guess at this point i would say that the pads are touching the disc, or there is something within the caliper making this noise. While spinning the wheel off the surface, try steering sharply one way or the other and see if you get the same noise from the rotor. Final point, the rotor is in no way wobbly is it? – Henry Jun 15 at 19:27
  • Okay I will look into if the pads have been installed correctly, I'm bringing it by the shop for the head mechanic to check out in a couple of hours. When I spin the wheel off the surface and steer sharply in either direction I get nothing, no noise. No, the rotor does not feel loose or wobbly. The noise doesn't happen all of the time, but often enough for it to concern me. I really appreciate your advice @Henry – Carman Cater Jun 15 at 19:38
  • It would certainly concern me, I wouldnt be happy with it making that noise. I would also make sure that you test it outside post repair, with the mechanic. Let us know what it was in the end! – Henry Jun 15 at 19:42
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The rotor might not be perfectly true. Although the shop should fix it as it's a new bike, do be aware that big MTB rotors get out of true really easily and at some point you just need to live with it. This can be somewhat mitigated with two-piece rotors utilizing a beefier spider, but in the end you're riding trails; stuff breaks all the time.

Is your thru axle tight? I know that with 9mm QR forks, violently turning and braking can sometimes be enough torque to momentarily twist the hub/dropout interface out of alignment, resulting in noise. A similar effect might manifest if your TA is not done up properly.

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  • Yes, the bike shop did look and work on it for free. I am going to add what I remember the mechanic saying he did to my original post. Yes, the thru axle is tight. – Carman Cater Jun 15 at 21:04
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That noise is a concern. It certainly sounds like something is hitting the rotor, but if the rotor is out of true you should get a periodic 'ching-ching-ching' sound. The noise is more random which makes me think something is loose, possibly the pad retraction spring has broken or come loose which is allowing a pad to rattle onto the rotor. Personally I'd avoid riding the bike until it is looked at by your bike shop. I'd be worried the pad might jam the rotor.

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  • I just got back from the shop, the head mechanic took the front brake apart and put it back together. I rode it around the parking lot for a while, and just now around the neighborhood. Seems that the noise is gone (for now!). I asked what he did, but I don't remember all of the technical details. Definitely re-aligned everything, tightened everything, mentioned something about [retracting?] the spring, etc. I wish I remembered more of what he said so I could share it here. – Carman Cater Jun 15 at 21:03
  • @CarmanCater if he mentioned a retracting spring I think I guessed correctly. There is a spring that keeps the pads held up against the piston. I think that came loose or broke in your case – Argenti Apparatus Jun 15 at 21:33
  • Yes, after speaking with my brother (who is a big rider and works on bikes), it definitely seems that the retraction spring could have been the culprit. I am going to get out on a ride in a bit, and if the problem seems to be solved I will go ahead and mark your response as accepted. I appreciate your time and well thought out response. Thank you! – Carman Cater Jun 15 at 21:54
  • I just got back from a test ride around the neighborhood. I can still get a slight rattle out of it when dropping the front end after doing a wheelie. Since the front brake has been rebuilt by the shop mechanic, I am not too worried about safety. From the feel of it, nothing is loose, and I have full stopping power. I suppose I will just have to learn about it on my own, and continue to investigate. @argenti-apparatus – Carman Cater Jun 16 at 0:33
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I have the exact same noise on a Cube Stereo Hybrid Race 500. It has the same model of brakes (Shimano BR-MT420) and 203mm rotors. Edit: The noise occurs most often at speeds above 20km/h and especially when turning. Sometimes also even when going straight.

For me the noise comes from the rear end. My bike is new with only about 180km on the clock. I took the bike back to the shop for a check-up and this is what they told me after making sure everything is aligned and there is no play in the hub.

  1. The noise is caused by the rotor touching the pads. The reason the noise sounds random and not periodic is because air escapes from the holes in the disc, causing vibration.
  2. The rotor, being fairly thin and cut out from a single sheet of metal, is almost like an instrument. If you flick it with your finger it will "ring".
  3. The noise is normal and should fade with use. (Not clear to me why it would fade)
  4. After alignment in the shop the noise was mostly gone but they told me it would likely return after some heavy braking.
  5. To get rid of the noise once and for all they said I could upgrade to floating Galfer rotors. I suppose other sturdier/floating rotors would also do the trick.
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  • Hi Mikko! Very interesting (same brake model). Yes, I've gotten a lot more riding time on the bike, and it will occasionally still make a tinny noise for a brief fraction of a second, but is fine other than that. I've ridden it DH as well as trails and everything seems to be working fine. I took it on the road between paths today and it made the noise at higher speed like you've said. If you end up really taking everything apart and find something please let me know! I've done it to mine and everything is in working order. Weird! :) – Carman Cater Jul 11 at 22:29

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