It is quite normal for ball type clutch release thrust races to be slightly pushed against the clutch tangs with the clutch fully engaged, thus the bearing rotates with the clutch but under very little load. If there is slight clearance then the ends of tangs on the rotating clutch will wear against the stationary release bearing. There may also be a slight ringing noise [caused by the tangs vibrating at high frequency] with a released clutch that goes away with a slight push on the clutch pedal as the clearance is taken up and the thrust race starts to turn again with the clutch. Of course any increase in noise as the clutch disengages is probably a clutch release bearing problem.
eg
http://www.british-cars.net/triumph-tr6-bbs/throwout-bearing-noise-200303231415551745.htmRegards PJB.
