Originally Posted by
FBinNY
A new hanger is no assurance of alignment, so check it either with a hanger tool, or at least by eyeball both vertically and (especially) for twist. Chain rub on the idler cage (if that's what you're describing) is a function of the alignment of the cage, and feeding angle of the chain.
It isn't rare and can be perfectly normal for some chain contact on the cage plates when cross chaining. From your OP it appears to be on the wrong side (... the chain starts rubbing on the bottom pulley inner plate when in big front ring and three big cassette rings.)is opposite to what would be expected with the chain coming from the outside w/respect to the cage, so unless you misdescribed the problem, I'd definitely suspect a twisted hanger or cage.
Thanks FBinNY, you seem like a good guy from your replies. I just thought the chain length might be the problem since that was the only thing that changed and I had no rubbing with the old chain. It is in fact the
outer plate that it is rubbing on. When I was looking at the diagram to get the correct name for the part (pulley inner/outer plate) it was drawn backwards. That may change things, but I do have another brand new hanger I can test with to see if I encounter the same problem. I will have to eyeball it since I don't have a hanger tool.