Rubbing sound from wheels when car is cold

[gwinder]

Last year during the winter after a 2 hour highway drive, as I exited on the off ramp I would hear and feel a grinding noise from the wheels as if the brake pads had froze on the disc. After a little while it would go away. Then all through the summer, no issues.
On Thursday, I went to St. Louis and as I came off the highway, I got the same noise again. Is it possible the brake fluid loses its viscosity when cold? The 02 X5 has 120K miles and as far as I know the fluid has never been changed?

Thanks

GW