When you turn on the bathroom sink cold water faucet it makes a thumping noise. If you continue to turn the faucet up the noise stops and the cold water flows full.

Close te angle valve under the sink and open it back all the way try it now if it the noise is gone you have a loose washer inside the angle valve, if the noise is still there you have problem with your cold side cartridge or stem washer, please tell us what brand and model faucet you have, Thanks.

John

Thanks for your response. Noise still there. Now I notice the stem is leaking. This is the stem that's coming from the wall. This would be the main water line... yes? Brand and model. This is am apartment house... no brand no model marked.

All faucet manufactures mark their products with their name. Sometimes on the handle, sometimes on then spout. Is this a single handle or a two handle faucet? Any idea how old it is? Can you give us anything to work with here? Regards, Tom