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I recently installed a rear luggage rack and washed my bike, and now I get a buzzing rattle when I ride over bumps in the road, independent of whether I happen to be pedaling at the time. It sounds like it's coming from somewhere below me as I'm riding, which probably indicates somewhere between the bottom bracket and the rear hub, or as high as the saddle. With my bike up on a repair stand I tapped the various components of the rack and tightened the screws but I didn't find anything obviously loose or that rattled as I tapped it.

How can I narrow down the source of the rattle?

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[Sheldon Brown -- Creaks, Clicks & Clunks](sheldonbrown.com/creaks.html ) is all you need, if it's coming from somewhere other than the rack. –  Nick Nov 2 '10 at 2:37
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3 Answers

up vote 4 down vote accepted

Since you don't hear the noise when the bike is up on the stand, the problem is probably linked to the load of your weight on the bike (trying to formulate this in a way that doesn't sound like I'm saying you're a problem or you're overweight but it's impossible! haha). Sit on the bike, swing on the saddle to simulate the effect of a bump and have someone check if there's anything swinging/bending and touching a part of your wheel.

If you're really desperate and have some time on your hands, remove the luggage rack and go see if you hear that noise. Then re-install it carefully. Actually you might save some time doing this right off the bat.

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Turns out it was my rack -- the metal strips attaching the rack horizontally to the upper part of the seat stay crossed and were hitting each other. While tightening the bolts I broke one of the bolts off, so now I'm down one brace until I get a screw extractor. –  Commodore Jaeger Nov 4 '10 at 3:01
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You can pick the bike up and bounce it from an inch or two. Check all the joints of the rack. You can check any and all bolts and tighten them, including bottle cage bolts. Remember to check the lock-rings on the valve stem of your tube. If those are loose they will rattle.

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Try the following:

  • Take your bike on your side, lift the rear wheel and let it fall from a short height, many times, while trying to find the noise;
  • Pull the bike along an irregular surface (rocky) and try to figure out the source of noise;
  • Grab the bike by the handlebars, brake rear wheel and lift front wheel until the bike stands. Then, make the bike jump like a pogo stick (specially good for noises in the front).

For any of these, if you have a friend to help you shaking the bike and/or listening, the more ears the better!

Hope it helps!

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