<sounds as if the head is hitting against the case or something. Now, <there is no disk access going on at all when this is happening, and it <happens regularly at (seemingly) random intervals throughout the day. All <of a sudden I'll start to hear the thunking sound and it will be coming <from one of the two machines' hard drive. Very odd. It may be that most of the non stepper drive will reseek from time to time to correct for temperature and wear. It's recalibration. Allison