Chain rubbing?

Hey

I fit a new chain (KMC X9), the other day, I put it against the old one and its the same size.

I have never done this before, and I think I have messed something up.

It seems as my chian is rubbing against, either my front mech, which is LX or my Crank teeth, which is LX as well.

This only happens when I am on a high geer and straight roads, so going really fast.

Can someone help, its a nice chain and I dont want to take it off, the gears are running amazing, but I hear the rubbing sound , What is going on?

Thanks again