"I'm not sure whether to call the water dept. or a plumber."

If only one fixture is having a problem it's very unlikely to be a water department problem, unless they have recently changed how they treat the water.

Has ANYTHING been change on the kitchen faucet?

Nothing has changed on the faucet. I thought it might be the old nozzle (to control water pressure), and removed it for awhile, but that made no difference in the bad taste coming and going. It's really a nuisance: I have to check the taste of the water before using it for cooking. If it's bad, I use water from a tap elsewhere in the house. It's very mysterious.

Does the water still have a bad taste even after running it for several seconds to flush out the nearest few feet of plumbing? Does this metallic taste come from both hot and cold taps on the sink? Is your plumbing copper or other type pipes?

Thanks, vgkg! I took a few days this week to "experiment", based on your suggestions. Yes, the taste comes out of both taps. It looks like the pipes are at least partially copper. The good news is that when I run the water for a few seconds the bad taste goes away. So I'm glad that's solved, though the reason for all this is still a bit of a mystery!