This solution word for me :
in Terminal make a directory called ".fseventsd" (mkdir .fseventsd) in the drive mounted by time machine, and add a file inside called "no_log" (touch no_log).
It tells fseventsd process not to bother reading the backup drive.
The annoyance ceased immediately.
Time machine backup worked flawlessly.
Solution found here : http://forums.macrumors.com/showthread.php?t=1103654