chain rubbing the front derailer

I am new to tuning my own bikes, and I am having a bit of rubbing of my front derailleur on my chain in certain gears. Any suggestions on fixing the problem or if that is even my problem. The bike is a 5 yr old cannondale r400 with sora and tiagra drivetrain.

Off to the bike shop, they will show you how to do a minor cable adjustment, probably just some cable stretch.

__________________
Cheers,
George.

what gears is it in when it's grinding? if both the front and rear cassettes are in their highest/lowest at the same time and there is grinding, you need to play with the high/low tension screws. every bike i've ridden has always had some cross-over grinding like when my crankset is in the lowest (inside) gear and my rear cassette is in the highest (outside) i always get some grinding now matter how much i fiddle with the high/low screws. just up/down-shift on the crankset when you start hearing grinding on the low/high gears

Willy nilly fiddling with front derailleur shift cable tension and limit screws is bad advice.

Go to the Park Tool website. Follow their instructions as if you were installing your front derailleur for the first time. Start at the very beginning and do all of the steps in order. The sequence of the adjustments is important because each adjustment can affect all of the subsequent adjustments.