ALWAYS... when a servo starts making a noise that is not normal for the servo... its a problem.
Digitals have a specific noise thy make. if you have any digitals, you most likely have 2 or more. if they sound the same they are probably OK. if one of the same make and model sounds different... you have a problem.
This works EVERY time.
ORIGINAL: fellers
ORIGINAL: FHHuber
Unusual noise from a servo means its time to replace the servo.
Absolutely untrue, in all respect to the tons of digital servos out. Digitals always make noise because they are constantly tracking their position. Standard servos correct around every 20ns i believe where digi is constant. My 1004SE Graphite can be a freaking chatter box at times, because every servo is digital.
A grinding noise on the other hand could be bad. like Hubber said, grind could equal partially stripped gear. Take it apart and look at your gears if it sounds like grinding or slipping and catching. Also always check to make sure your servo horns are tight. They will ocasionally work loose , especially plastic.