Why do my front wheel/disc brakes squeal/moan when NOT braking 1 year old Trek 520 with mechanical disc brakes.
When I am pushing the bike around, both with and without loaded panniers, the front wheel frequently makes a low pitched &quot;squealing&quot; sound--almost a moan.  With the front of the bike lifted off the ground, the wheel spins freely, with no apparent interference.  There is no noise or any apparent problem.  The noise appears to be accentuated when the wheel is not aligned with the bike--ie, turning left or right, but it can happen whether straight or turned.
The brakes seem to work fine.
There is no obvious sideways play in the wheel.
Since the brakes seem to work fine, and the noise doesn't happen when riding, I've been riding anyway--but I'm concerned that there might be some brake issue or something else I'm not thinking about.
What else should I be thinking about/checking?
One of the pads is lightly touching the rotor. When you push the bike at low speeds the pad makes the rotor vibrate at a resonant frequency - like a bow on a violin string. When the rotor rotation speeds up the resonant frequency isn't excited any more.
The pad can be touching lightly enough that there does not appear to be any resistance.