Where is the chain rubbing the cage? Can you take a picture of the crank (preferably with the crank facing the camera straight on) with the chain on the big and middle rings? Also, take a picture of the alignment of the chain inside of the derailler cage.

Switching to a double won't help you at all, especially if you don't already know how to set up a front derailler.

One last thing, just FYI. The derailler type you have is a braze-on.