Sulfer Smell in Bathroom Faucet

One of my bathroom sink started to smell like sulfer when the faucet is turned on. The smell doesn't appear to be in the water, but it seems to begin when the faucet is turned on. The smell lasts about 10-15 seconds. Another oddity is that it doesn't happen all the time, but perhaps 60% of the time. I live in a condo unit that's upstairs. All piping on the faucet appears to be in good condition, including the P-trap, which I'm starting to learn about.

I have not had the same experience in my second bathroom or the kitchen.

What could be causing this smell and what can I do to fix it?

Sulfer Smell in Bathroom Faucet