I recently bought a new mountain bike and when I pedal, sometimes (almost randomly) I will hear a clunk or a knock come from the bike.

It usually only happens once or twice, but I worry because it sounds like something is wrong.

I haven’t been able to diagnose the noise so I require some help, I can’t find anything else about it anywhere.

Here is my best shot at uploading a video https://drive.google.com/file/d/1cejCxh3UrFvfgYRZ9a88fZx6ZsWCs5Ym/view?usp=drivesdk

  • Hi, welcome to bicycles. Is there any way you can post a video that demonstrates the sound?
    – DavidW
    Commented Apr 10 at 23:26
  • Aside - you appear to have created a second username by mistake. Try to use the original username You can merge your two usernames at bicycles.stackexchange.com/help/merging-accounts
    – Criggie
    Commented Apr 11 at 23:53

1 Answer 1


If it's only when pedaling I would guess it's coming from the bottom bracket. After a wet ride or washing your bike water often penetrates the bottom bracket and allows things to shift slightly making the knocking sound. Usually worse on one side or with more power. A quick clean and some grease is the solution if so.

  • 1
    I guessed that too, on mine, but in the end found it was a saddle bolt. So while this answer is quite likely, you need to look at everything
    – Chris H
    Commented Apr 11 at 7:05

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