Hi, I have a problem with my brand new rear derailleur. The chain rubbing on the left side of the long cage when I have my gears on the biggest chainring and the 2 biggest cassette cog. My setup is a 7 speed with a XTR crankset, XTR front derailleur and mega 9 XT rear derailleur. I was thinking about putting spacers in the pulley screw to make the cage more wider but if there is a way to fix it without any modification, I be more than happy to try it. Any idea guys?

PS: I was thinking that the problem is my chain. Because the XT derailleur is made for 9 speed, I figure that a 9 speed chain is more narrow than the 7 speed chain. Reason why it is rubbing against the cage.

Thanks