Have you determined where it is rubbing? Hard pedaling in the small ring will cause the chainstays to deflect, which in turn can cause the chain to rub on either the front derailleur or outer ring. If it is the front derailleur that is rubbing, a little trim can fix that. If it's rubbing on the ring, that will be harder to address, and you may just have to live with it or avoid hard pedaling in the small ring.