Can U Diagnose This Problem? Funny Noise

The first thought that came into my head was a loose spoke, too, but you checked them. I had a mystery metallic noise once, too. Turned out that my cassette lock ring had somehow worked itself loose.

"The sound repeats faster the faster I go. The sound continues whether I'm pedaling or not" - means it has to be related to the wheels going round.
If all spokes are healthy and there's nothing touching the wheels as they rotate, the only thing I can think of is a damaged bearing or a busted axle.

At slow speeds, mystery sounds CAN be caused by something loose either inside the hub or inside the rim, a ball bearing gone astray or a nipple dropped into the rim at build etc. But at higher speeds, rotational forces tend to stick these in position, making the noise disappear.

nice information
thanks

Thank you folks.. I directed the professional mechanic who did my recent tune up to the the rear hub. To add insult to injury I got a flat on the way home (my second in two days) so I am upgrading my Bontrager 700x 32 stock tires to Gator Skins 700X32. Should help with the flats.

It should be ready by Thursday night!

My guess is that it's coming from a rear spoke. Even if the spokes seem tight enough, a slight bit of corrosion or dirt at the X crossing (mid-spoke) could cause the "tong" noise you describe as a spoke goes round under load. Your mechanic should check the spokes by squeezing each crossed pair together. If that's it, a drop of oil on the spoke junction will usually silence it.

OK I got the bike back. He repacked the rear hub and tightened the spokes as well. Noise gone!!! Wahoo