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It's kinda hard to describe but there's a sound coming from somewhere on the bike when I pedal hard - I can't figure out where it's coming from. It's sort of like a high pitched pig squeal. It started happening randomly really and hasn't stopped since. If anything, it's been getting louder.

Any ideas on what it could be?

How can I narrow down where the sound is coming from?

  • Is it more likely when you've just pulled away from a stop? I'm thinking a brake isn't springing back properly, perhaps combined with a wheel that's not running true. – Chris H Sep 1 '16 at 11:35
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    I would guess that the frame is flexing and causing either the brakes to squeal or the tire to rub against the frame. First make sure your wheels are securely bolted in place and make sure they are centered and not twisted off to one side. And inspect your frame for cracks, particularly the "down tube" that runs down the front. – Daniel R Hicks Sep 1 '16 at 11:43
  • Try and wriggle your pedals by hand. Not around but side to side. Is there movement? There shouldn't be. Bottom bracket loose or getting worn can cause interesting noises under load. Tightening up bottom bracket might solve problem if loose OR might temporarily/partially solve problem. You would need to replace bottom bracket on any bike after a few years of pedalling. – gaoithe Sep 2 '16 at 11:09
  • Can you attach an audio recording or video of the squeal? – RoboKaren Jul 30 '17 at 19:04
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    I rolled back the edit that deleted all information about the actual noise. Come on, OP -- your edited question was completely unanswerable. – David Richerby Aug 2 '17 at 11:37
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This sounds like a bottom bracket bearing.

Check for looseness in bottom bracket by wriggling your pedals. Do they move in ways that they should not?

When the bearing housing fails, you both lose the glide of the bearing and also introduce bits of 'shrapnel' into the bottom bracket which rub and squeal with each crank, as the bracket deteriorates further, the noise and friction will increase. However, at some point, you'll grind all the shrapnel into shavings and will have scored the interior of the bottom bracket such that there will be more room and it will become easier to pedal and quieter, though it will still be far more difficult than a working set of bearings. Bottom brackets are easy to inspect and replace. Good luck with the repair.

  • Sounds like bottom bracket to me too. Wriggle your pedals. Are they loose in the bottom bracket? Tighten bottom bracket or replace it. Have you been cycling bike a long time without replacing BB? Also see here: sheldonbrown.com/creaks.html – gaoithe Sep 2 '16 at 11:14
  • Wouldn't a BB be a sqeeek-squeek rather than a squeeeel? – RoboKaren Jul 30 '17 at 19:05
  • @RoboKaren it would depend on how the BB has failed. – J.P.M. Jul 30 '17 at 19:07
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    Check for looseness in bottom bracket by grasping the cranks and feeling for play, not the pedals. – Argenti Apparatus Aug 2 '17 at 15:03
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I know this is an old thread but I thought I’d add my 2 cents. You might want to lube your rear derailleur jockey pulleys. That’s where the sound was coming from on my road bike. If it doesn’t eliminate the problem at least it eliminates one possibility.

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From my experience, this sound comes from crankset/crankarm, that is not tightened properly on the bottom bracket axle.

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    this happened to my bike many times. Tightening the crankarms fixes it. – Tooniis Aug 8 '17 at 9:52
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This is a hard problem to diagnose since its related to a heavy load on the pedals, then you can't look for the cause with the bike in a stand because it won't exhibit.

Some things to try:
Test the rear rim brakes (only) by going somewhere quiet and unhooking the rear brake, then try a powerful start and see if it squeals. Then hook your brakes up again immediately.

Do you have mudguards/fenders? Check for witness marks anywhere that might be close to a wheel.

Give your rear wheel a wiggle - it could be a loose axle contributing to some movement.

Frame flex -Stand over the bike and with both brakes hard-on put some load on a pedal in the horizontal position. Look straight down and see how much your frame flexes. This will give you some idea about how much variance it has when you press really hard.

I have a bendy steel rigid MTB with home-made mudguards. Under hard pedalling it make a buzz noise as the knobbies rubbed on the plastic used to make the guards. Turned out there was sufficient frame flex under load to make the rear wheel contact the guards, but not enough to find it in the workstand

Squeals tend to be brakes or bearings because most rubbing noises sound exactly like rubbing noises. A squeal is higher-pitched.

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