New
#11
Use chkdsk /f /r on the external drive, just in case there's bad sectors and that's what's slowing down writing/reading from it on shutdown.
If the external drive is there for backup purposes, it should be disconnected from the computer at all times when you're not backing up (otherwise it's not really a good backup - it only covers HDD failure in your main machine, not lightning strike/surge/theft/PSU-fail/cryptolocker/etc).