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There is a very loud screeching noise when i pedal hard on the down stroke. Be it moving off or climbing up a hill. It is not coming from the front wheel, which i originally thought came from brake rubs, because when the sound still arises when i put my bike on the trainer. i am pretty sure it comes from the bottom bracket and only arises when i pedal hard. if i am coasting at 30kmh, there are no sounds, but if i pedal hard to raise the speed, then the loud screeching noises will arise again. please help! thanks

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Not a good sign. However, be aware that it's often difficult to tell the difference between BB noise and pedal noise. Also make sure that there's nothing that the chain ring may be rubbing against (check the inside of the chain ring for marks that would indicate rubbing, in addition to looking for stuff that might hit it). –  Daniel R Hicks Mar 14 '12 at 15:24
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Could you post photos of your BB area, from different angles? (edit the question and insert them there) –  heltonbiker Mar 14 '12 at 16:13
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Or you could insert links to your pictures and we can insert them. (Low-rep users can't insert actual images yet.) –  Neil Fein Mar 14 '12 at 16:19

1 Answer 1

With this level of information, the only good answer is to say,"Find a competent bike mechanic, and ask them to look at it."

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