Earlier this year we replumbed our our whole house with PEX. We have three bathrooms, one on each floor. About 6-8 weeks ago we started getting a sulphur smell in the upstairs vanity water lines when we turned the water on. There is no smell in any other water line, including the toilet and shower in this bathroom. It's in both the cold and hot water lines. After running the faucet for about 30 seconds, the smell goes away. Do you have any idea what might be causing this?