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My back wheel is giving out a periodic squeak as if the wheel were buckled and rubbing on the brake. Only, it's not buckled and it's not rubbing on the brake.

It's one squeak per revolution of the wheel, regardless of speed, but each squeak is the same (short) duration even if I move slowly. It doesn't matter whether I pedal or coast. The wheel isn't rubbing on the frame and if I gently brake through several revolutions it still squeaks while I'm braking.

I asked a bike shop about it a while back and they couldn't find anything but after all the routine adjustments it went away for a while. Now it's back.

If I get off and turn the wheel by hand there's no sound. Even if I lean on it and roll it around it's quiet. It seems that I need to put all my weight (an my panniers and gym gear) on it to make it squeak. I guess that's why they couldn't find it in the shop.

My best guess is uneven spoke tension might allow some of the spokes to shift and rub slightly. I've looked them over and don't see any wear and I'm not sure how I'd make a definitive diagnosis there.

What could it be? What else can I test?

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    Are you sure that the brakes or tire are not rubbing somewhere when sitting on the bike? (e.g. have you completely disengaged the rear brake so it can't possibly rub and see if the noise comes?) A shop should have a spoke tensiometer, but that would be more of a clink than a squeak for low spoke tension. – Batman Nov 24 '16 at 6:26
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    @Batman, well, I reason that by braking gently so that the brake is always in contact with the rim, that the noise should go away or be continuous. Although, thinking about it harder I guess it's possible that the edge of the brake clips a lump in the tyre and rim contact doesn't change that. – sh1 Nov 24 '16 at 18:41
  • Hang the bike up on a rope or a workstand, and look closely at the contact points through the whole wheel rev. Do you have access to a spare wheel to swap out - just for a trial? – Criggie Nov 24 '16 at 19:12
  • Try squeezing pairs of spokes together to see if you can spot a loose one. Try to use the same finger pressure (not much) on each pair, and test each spoke against it's two neighbors. If the cause of the squeak is a loose spoke then it should be fairly obvious. Another similar test is to tap each spoke with your fingernail and listen for differences. – andy256 Nov 24 '16 at 21:56
  • Yeah, one possibility is that the tire is bulging out and a brake pad brushes it, without being close to the rim. But in this case the squeak would likely change or stop when one applied the brakes. I'm guessing this is a bad bearing. – Daniel R Hicks Nov 25 '16 at 0:10
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It could be the freewheel or hub bearing causing the squeak but this should not be the case as both are lubed, or should be. More likely is as you mention a spoke. Sometimes spokes squeak at the hub end as they flex.. Try rubbing in some grease or putting on a drop of oil on each spoke fitting at the hub end to see if it cures it, just ride the bike and let the lube take effect. Of course a spoke could also squeak at the nipple end too as it flexes slightly in the wheel, the only way to address/lube this end properly is by removing the tyre etc and applying a tiny drop of oil to each nipple. Don't let it get near your braking surfaces though.

  • Hmm. Spokes shouldn't be loose enough to move. It seems to me that oiling them is treating the symptom, not the cause. – andy256 Nov 24 '16 at 21:59
  • Spokes can and do move but only very slightly as a wheel rotates and is loaded in different positions. Also a wheel flexes with lateral loads too which loads one side of the wheel whilst unloading the other, this creates friction points. As there is quite often torsional stress in spokes too this can cause movement and noises like squeaks, especially at the hub end of the spokes as the steel spokes and alloy hubs interact with each other. The minute stresses and friction at these points can be the causes of noises and squeaks too. – Orb Nov 24 '16 at 23:52
  • Unless the bike is radially spoked (quite unlikely on a rear wheel), the most likely source of spoke noise would be where the spokes cross. This is fairly easy to diagnose by working small pieces of something (eg, tag board) into the crossing points, to see if the noise goes away. Some folks have been known to permanently install small pieces of leather at the crossing points, to eliminate the noise. – Daniel R Hicks Nov 25 '16 at 0:14

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