I have lost practically all water pressure in one of my bathroom sink faucets. There is barely a trickle of water coming out. The other sink and the tub in that bathroom work fine. My house is about 30 years old, and there are no shut off valves under the sink, so I know the valve didn't accidentally get shut. Does anyone know what would cause this?

My home is 15 years old, slab construction. When I run one of my outside faucets, I get a knocking noise (vibration). Everytime I turn in on and off, I get this noise for a few seconds. And, when the water flows at a certain speed (about half way on), the knocking will be consistant. Sometimes the vibration is so bad that it runs through the slab into the kitchen (about 30 ft away), and causes the kitchen plumbing to vibrate. 1) What causes this type of knocking? 2) Is it bad for the plumbing/slab? 3) How can it be corrected? 4) Would it help to replace the faucet? Any help would be greatly appreciated.