It is possible that the chainstays on your frame are so short that the derailler cannot be positioned to allow for noise-free operation in all gears. Possible, though not likely.
There are a number of causes of chain rub on the front derailler. Start with the high stop screw. Make sure that it is set such that you have just enough clearance in the 50/12 combo to not have chain rub. Any excess clearance on that end will reduce your clearance when using the larger cogs. Next, check the angle of the cage. You want the outer cage parallel to the chain when using the 50/12 combo. If the derailler is angled any further out than than it will again reduce your clearance when using the larger cogs. The derailler height might also be a factor depending on the shape of the inner cage. You'll want the derailler positioned as close as possible to the top of the larger chainring in order to maximize clearance (assuming a shaped inner cage. Not being familiar with DA7900, this may not be applicable).