Originally Posted by
HillRider
If the chain was originally sized to allow a 53/34 big-big combination it could indeed go completely slack in a 34/11 or 34/12 combination.
Yes, but my comment still applies. A long chain would not cause rubbing on either the chainwheel or front derailleur cage (unless you count slapping against the outboard chainwheel from swinging back and forth). The only noise in such a case tends to be a rattling sound from pulleys. Again, we need the OP's observations regarding where/how the rubbing is occurring.