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On bumps a very loud click sound comes from somewhere on my bike.

When I have my weight on the seat and there is a bumpy road, it's a scary loud noise since 2 days. It developed slowly since one month until it has become a scary sounding fraying cable / floorboard sound.

I touch my hand on the top tube and I can feel little hammer hits inside the horizontal top tube when i press back/down on the seat post, as if the top tube is generating a stretch stress sound.

Front forks and head tube and bearings seem perfectly sound, checked them. The crank is fine. The back is fine.

Has anyone encountered something similar? How can german Aluminium MTB make scary crack sounds? What zone of a bike can do that?

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    Sounds can come from many areas. My first suspicion would be the seat springs, but could be a cable housing banging the frame, or could be a crack in the frame. And a dozen other things. – Daniel R Hicks Oct 17 '17 at 20:47
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    What does German have to do with anything? – Batman Oct 17 '17 at 22:47
  • Can you replicate this noise when not riding? IE can you sit on the bike and put a shove into the saddle using your bodyweight? If so, get someone to watch closely and isolate where the sound comes from. – Criggie Oct 18 '17 at 4:12
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    I took the seat post out and pressed the seat bracket, it still cracks, it's coming from the top tube as far as I can see. its tremendously loud, not the cables... the clank sound is the loudest in the top tube. I have a second copy of the same bike, it's done 10k miles on flat and 1k miles of MTB. I was qualifying the bike as a german aluminium bike, aluminium is not springy, it does stress fractures, but the sound i am hearing implies a 1mm percussion effect inside the metal someplace. ill probably change the bikes over and do some thorough tests on it. – com.prehensible Oct 18 '17 at 12:16
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It was the rear suspension bearings, I placed WD40 on them and it was fixed. It seems that they were stiff enough to be jumping around same as a stiffly creaky door rather than actually turning.

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    Wd40 is a very poor lubricant and can flush out the remaining good lubricant. I’d recommend you get the bearings rebuilt and repacked with a good grease in the near future. – RoboKaren Oct 19 '17 at 16:10
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    It’s not you-will-die-critical but for-best-performance and to-prevent-further-damage-important. – RoboKaren Oct 19 '17 at 19:33
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    +1 for coming back and telling us what you found. You can mark this one as the "accepted" answer because it shows the question has been resolved. Good work ! – Criggie Oct 19 '17 at 22:34

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