Chain rubs on front derailer
 

Recently i bought a rockhopper and notice the chain slightly rubs against the front derailer, but it only does it on 2nd 3rd gear of the front dearailer.

It happens on most bikes, just something you will need to get used to. You can spend countless hours trying to adjust it perfectly (I've tried) but you will most likely still end up with slight rubbing. It doesn't hurt anything as long as it is just slight. If it gets worse take it into you lbs.

You do get that because the chain sometimes comes on a angle and is not 100% straight so it rubs slightly against the front derailleur.

Does it happen when the bike is 2nd or 3rd gear in the front regardless of the gear in the rear? Try going HERE and read the What's what at the bottom and see if that could be your problem...

If you learn some basic bike maintainance skills you can save yourself a ton of time and money. You just need to loosen the cable and pull it tighter or looser (whatever it needs). A simple fix. And some things you need to learn WHEN (not if) you have some mechanical problems out on the trail. I don't mean to come across as a bunghole, just trying to help.