That's not a sound that anybody likes, but it really doesn't hurt anything except perhaps your manicure; however, when the brakes on your road bike make a similar sound, it's time to take a little action.
When you hear a hissing, grating sound as you apply your brakes, you've likely picked up some sand, gravel, glass or other road debris and it's become embedded in your brake pads. Left alone, it may get worn down, polished, whatever, so that the noise abates, but you've still got an abrasive working on the braking surface of your sweet wheelset. The solution is simple and, yes, kids, you can try this at home! Brake pads are easily removed by loosening the small hex head set screw (you don't have to remove the whole brake shoe-just the rubber pad) and sliding off the pad. Remove your wheel to make it easier and the front brake may require you to squeeze the lever to allow the pad to clear the fork. Inspect the pad and gently pick out any hard stuff that has worked its way into the surface. It will usually appear silver, just about the color of your $1000.00 wheels. I use the point of a small pocket knife. While you're at it, clear the crap out of the sipes, or grooves in the pad. Replace the pads and tighten the set screw. Done.
By just removing the pads, you don't have to reset the brake position, so it is a very simple proposition that will extend the life of your wheelset and add peace to your ride.