When your hard drive begins to make noises you need to buy new disks (same or bigger size) and clone them sector by sector to save the data on the new media.
Noisy disks usually mean that the hardware (disks) are starting to fail. My guess is that you have a failing external hard drive.
This happened to me and the DMI data base would loop on boot up - either until it did manage to boot the system or kept on looping. A trip to my vendor advised me to ghost the drives (I had two at the time), and now have four include the ghosted (cloned) drives from my previous system.
Newer disks usually have S.M.A.R.T. hardware detection for the health of the system. You could download a Linux Live CD, burn it to CD or USB and boot the Live system from that media, and then run the System>Administration>Disk Utility to see the SMART health of your disks. Live systems do not mount your hard drives unless you issue the mount command as root (admin) user.
You can use the dd command (as root) from the Linux Live CD/USB to do the sector x sector copy from your unmounted external hard drive to your new drive - hopefully if it can be read. If it can't be read, then it may be toast - all the more reason to adopt a procedure/process to daily, weekly, monthly backup your hard drives.