The noise on your external hard drive may be indication of a BAD sector on the hard drive. Try running a full checkdisk/scandisk on it including testing unused space to mark the bad sector.
Note to others: If it is not a external Hard drive, it is not recommended to defrag. USB thumb drives usually use a method to reduce the number of times each memory location is written to increase the life of the thumb drive due to limited number of writes before the drive fails. Defragging a usb key should be done sparingly at most.
Sincerely,
TurtleWax