A bicycle truth: every strange, hard-to-find noise will eventually be traced to a bearing.
I've had this annoying, subtle, erratic noise on my Specialized Tarmac the last 2 weeks. Sort of like pinging spokes, but not quite. Rotational for sure. Any gear, coasting or not, noise increased when riding no-handed! For sure it was coming from the front
Finally, I figured it out: it must be a small loose piece of metal inside the aero part of the rim. Took the tire off and blew the rim out with compressed air. No change. Finally, I swapped the front wheel out - no change. Swapped the rear wheel out - noise gone. Took a closer look and the axle nut was loose ?! Further looking and found the derailleur hanger was loose ?! This hub (Roval with Dura-Ace cassette) has a single, full-width sealed bearing. Anyway, everything is tight, right, and Loc-tight now. Not the bearing itself, but the nut holding it in place. Problem solved!
