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Grinding noise!


MTB_Trials_and_DNB.
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Hi all,

My first post here, sorry if it’s in the wrong place.

recently, after a 20 year gap, I brought a trials bike again. It’s an echo GU 24” and I love it. Absolutely loving getting back into things, especially as previously I was rather young with little money and my bike was more like a tank 

I recently got a puncture and had to remove the back wheel. since resolving the issue, I’ve had a strange noise which I am struggling to understand. 
 

the noise is a very dull grind and a small vibration which can only be felt while spinning the back wheel, while it’s lifted off the ground. 
there is no noise or vibration when any pressure is on the cranks. The noise doesn’t occur when the wheel is spun backwards. 
 

I’ve taken the tyre, tube off and chain off and spun the wheel in the drop outs - no sound or vibration. I’ve checked the BB by spinning the cranks - also no sound. I’ve check my wheel is in straight and there is no pad connection to the rim. The wheel is pretty true, a very faint wobble. 
 

I noticed a couple of things today firstly that the chain slack point causes a little wobble of the chain when coasting. This seems to be in Rhythm with the vibration and the sound. I’ve also noticed that the chain right (potentially not the correct terminology is not a perfect circle around the cranks (I’m not particularly sure this is the issue or if it’s even possible for a perfect circle) it’s a very small increase in the gap between what holds the chain ring and the cranks. I’ve added a picture of what I am talking about. The increase in gap size is marginal. 
 

my feeling is that it’s the chain loosening off and increasing tighteness and the wobble which comes with it that is causing the issues - I think this as the issue is not present under pressure to the cranks (chain stays tight obviously). 

that said, I am not sure and it’s a little unnerving. I am not so worried about the noise and the vibration if there is no need to be, I’m worried about catastrophic failure of moving parts while riding. 

any ideas or thoughts would be appreciated! 
 

thanks 

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Thanks for the vids - I hear it, perfectly normal. The freewheels use open bearings as you can get twice as many balls in as a sealed bearing (thus better load capacity), but with no seal you can then hear everything that's going on inside. There is always a very slight variation in chain tension with a tight chain and horizontal dropouts, hence the 'on-off' noise as the bearings load and unload. It can be quietened by filling with grease, but then you risk gumming up the freewheel mechanism.

Any skipping or stuff like that isn't good, but all safe to use as is B)

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