Just got a new bike from LBS: Trek Lexa SLX C (compact), and I got a question: When chain is on the largest cog in front, and smallest cog in rear, and it was rubbing the cage. Actually, the chain will start rubbing the outer plate of cage when rear gear was on 7th gear,... and this is not "cross chain", and am I correct? Already went to my LBS, after 20min., they said it's been fixed.... Only to find out the issue still the same after I got home. Is it something that I can learn to DIY to fix? Any advise, and comments are appreciated!