Originally Posted by alfeng .
The good news is that MOST seemingly random noises can eventually be isolated & they usually can be eliminated ...
Without seeing your bike, the noise is possibly due to the chain rubbing against the FRONT DERAILLEUR CAGE despite your impression that the noise is coming from the rear of your bike ...
Appropriate adjustment will hopefully eliminate the rubbing ([COLOR= rgb(128, 128, 128)]it could be as simple as removing the slack in the front derailleur cable when the chain is on the inner chainring ... with the result being the outer plate being about 1mm further outboard rather than possibly rubbing against the chain[/COLOR]).
If necessary, check www.parktool.com and/or YouTube for assistance. BTW. If your bike has a SRAM drivetrain & you encounter difficulties then you may be SOL because Front Derailleur adjustments are limited with SRAM shifters ... but, they can eventually be made if you have the patience ([COLOR= rgb(128, 128, 128)]again, check the front derailleur cable tension when the chain is on the inner chainring, [/COLOR][COLOR= rgb(0, 100, 0)]first[/COLOR]).