This subject has arisen more than once on this board, and I thought
that a stuck caliper was bound to be the cause. (The squealing was
only when the car was rolling and the brakes were not applied.) Also I
had found that lubricating the caliper slides fixed the problem -- for
a while.

Recently, however, I bought new wheels with my new snow tires and
mounted them myself, being careful with the torque wrench on the
lugs. To my surprise, the squeal has gone away.

I think somebody posted a short note the last time the subject was
raised, saying "I'll bet it's the wheels." Turns out, he was right --
at least in my case. I guess the compressed air wrench the previous
guy used in mounting my tires warped the disk.

Thought you'd like to know.