Kitchen Tap Water Smells for 15 Seconds?

For the past two months our kitchen faucet water has started to smell like decayed organic matter. It tastes funny too. But it happens for only the first 15 seconds or so. We use the water after we let it run for first 15 seconds. We also checked all the other taps in our home, but none of the other taps smell.

We have had many plumbers come and check our water softener, water heater, and pipes. Nothing came off it. We called the county too, but they cannot help since no one in the neighborhood has complained. It looks like it is a highly localized problem only in our kitchen tap. We changed our tap too, but the smell persists. What could be the problem? Is there anything else we can do to help solve the issue?