At one time or another most people have experienced a faucet that whistles. While annoying, this problem can be fixed without too much trouble. Normally a faucet whistles because of a bad washer in the faucet. Replacing a washer in a faucet takes only a little preparation and about half an hour, even for the novice.
Shut off the water supply to the faucet. Turn the shutoff under the sink all the way to the right for the handle that the washer is being replaced. If there is no individual shutoff under the sink, then close the house's main shutoff valve.
Remove the button cap on top of the handle by prying off with a screwdriver. The button cap usually has a "C" for cold or "H" for hot imprinted on it.
Unscrew the screw that sets under the button cap and remove the handle.
Extract the washer, which should be visible. A pair of needle-nose pliers works well for pulling out the washer.
Install the new washer using needle-nose pliers to set it into place in the faucet handle. Make sure the washer sits in place just as the old one did.
Reassemble the faucet handle by reversing the process used to take it apart. Turn on the water supply.