Scratched Wheel

you can readily sand those to the point where they're not an issue. You don't need to go as far as 2000 grit (that's virtually polishing. 400 grit sandy will be fine. It will probably take bout 5 mins

Without seeing the wheel we can't tell how deep the scratch is, and thus you'll get folks telling you to replace it which may not be necessary.  I scratched a brand new wheel so deep that the brake pad would jerk on it, but instead of replacing the wheel I fixed it, and this is how I did it, actually there are several ways to do it, all are usually right, this is just the method I used.  

First of course is to remove the tire.

I took a fine tooth flat file and gently went over the scratch area to knock off the rough spot.  Next I took 2000 grit sand paper (3M is good stuff) and I sanded it till the scratch was barely noticable, it was still there but the brake pad no longer grabbed it.  I then took a Scotchbrite pad and went over the entire rim with it to even out the look of the newly sanded area.  That's it, easy peasy.  Again the scratch was still there after all of that but since the brake pad was no longer grabbing it I felt I didn't want to sand it down too far, and besides now after 8,000 some odd miles later the action of using the brakes has rubbed it down to where I can longer see it.  

That method I used is the same method that I used back in the day when there were seamed rims, minus the file, I had to sand down the seam on new rims so the brake pad wouldn't grab the seam.

Of course is the scratch is real deep then the wheel may have been compromised.  I would try the method I gave you above and see what happens, if after a lot of elbow grease it's still deep then take it to a LBS and have them check it out to see if it's too deep to fix.

Can you upload a photo of the "scratch"? What kind of "light" noise - squeal, howl, shudder?