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My rear derailleur is making some noise and I'm having trouble diagnosing the cause. It seems like it's coming from the rear cogs and sounds similar to chain noise. I'm re-building my bike after an accident, so it's possible that something was bent though I don't see any gross damage to the RD. I've spent some time browsing this site and others for ideas, and have checked the following:

  • Checked hangar alignment
  • Lubed the rear cogs
  • Lubed the chain
  • Checked the b-limit setting
  • Indexed the gears & ensured they shift well
  • Checked for chain stretch (chain only has ~250 mi on it)

Can you think of any other causes for a noisy rear derailleur? I have a video if it's helpful.

EDIT: Thanks everyone for the help and suggestions! It ended up being a combination of a bent hanger and a twisted derailleur cage. I replaced the hanger with a new one which helped to reduce the noise, but there was still some prominent noise coming from the jockey wheels, mostly on the smaller cogs, and only when in the large chainring. I changed the derailleur and the noise is now gone.

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    Sprockets do not need to be lubed, just the chain. – Argenti Apparatus Aug 13 '18 at 15:45
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    The video would be more helpful if it showed the shifting straight from behind such one could observe how the chain sits on the cogs and the overall alignment. – Christian Lindig Aug 13 '18 at 19:54
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On checking the hanger alignment, A, how did you check? There are alignment tools for that. B, Did you check both "twist" and "bend"? I.E. Looking from behind, is the hanger straight down, or in toward the wheel ( bike was in an accident, usually, they get bent inward ). That is "bend", twist would be looking from above the bike down to the ground, is the front of the hanger closer to the wheel? It is hard to tell without the tool, unless the bend is severe. Next, in the accident, could the rear derailleur have gotten bent itself?

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  • Thanks for the suggestions, it ended up being both the hanger and the derailleur itself. Replaced both, and the noise is finally gone. – James Dolezal Sep 2 '18 at 17:10
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Check for hair, grit, etc caught up in the derailleur wheels; most likely the guide pulley wheel; remove both wheels: attach the tension wheel last after cleaning/oiling.

Make sure you pay attention to which wheels go where; and the direction arrow on the tension wheel. A google search will show you a diagram of both wheels labelled and the turning direction of both wheels. eg. guide wheel is the largest wheel located nearest to the cassette. Both wheels should have labels `etched' on them.

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If you don't have an alignment tool for the hanger you could maybe use an old wheel with a threaded axle if you have one available. The axle should fit the derailleur hanger thread.

Most often the hanger is bent towards the wheel. A clear sign of this is if the gear change works well with the smaller cogs but the derailleur moves a little bit too far on the bigger cogs. Because on the smaller cogs the lever of the derailleur cage is shorter and so is the influence of the misaligned hanger. But on the bigger cogs the influence is bigger.

So if you setup the derailleur for the smaller cogs and the noise becomes louder when switching to bigger gears or maybe even changes two gears at once then it's most probably a hanger which is bent to the inside.

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Chances are that the derailleur cage is slightly bent or that you are using a wider chain than the optimal. Chains that are used for 6 to 8 speed bikes are wider than chains used in bikes that have 9 speeds, and even wider than bikes with 10 or 11 speeds.

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