OK, here's another problem.
I own a 1996 (or so) Jamis Dakar Team frame. I like the frame a lot, but it was not disc compatible. So I bought an adapter made by a Taiwanese company called A2Z (you can see these on it's website, and frequently on ebay). I have the Avid mechanical disc brakes attached to the adapter. The hub is a Magura Louise Pro. So the disc seems to make a light rubbing noise--"cling, cling, cling". It does this entirely randomly. The bike will go for miles of silent operation, then this noise will start. Then stop. Then start again. The length of time that it continues varies from a few rings, to a very long period. It does it sometimes after the suspension activates over a big bump; sometimes not. It activates sometimes after a tight corner, sometimes not. The ringing noise seems to be more active when there is a little less pressure in the rear shock. It's not a bent rotor, or it would make the noise most or all of the time. I've tried positioning the rotor further away from the frame by eliminating a spacer between the rotor and the hub shell (the rotor was very close to the left chainstay). That did not eliminate the problem. The ringing noise only happens to when I'm riding the bike, but never when the rear wheel is spinning with no weight on it in the repair stand.
I realize that using an adapter on this frame is not the ideal solution, but the ringing noise is mystifying, because I cannot detect it's cause, and it is so random. The only other solution I can see is that the bushings in the rear suspension are loose, but I can't detect any play in the rear triangle either.
Anybody want to take a guess?