I hate to tell you this, but I think your drive is almost dead or you controller is going bad. I would recommend getting a backup of it ASAP. You can use Déjà Dup, its included in Ubuntu. Also you may want to run a disk utility to check you hard drive, depending on the manufacturer, most of them have testing utilities. Also you can try a different hard drive if you have one handy. Again make sure you get a backup ASAP, before the drive gets any worse. Good luck.

Déjà Dup is a simple backup software for Linux. It hides the
complexity of doing backups and uses duplicity as the back end.

Déjà Dup takes the simplistic approach, and presents just two very
large buttons - Backup and Restore. Swipe one (you really can't miss
them) and Deja Dup will do the rest. Except, you probably do want to
play with the configuration first, such as setting a backup
destination, whether you want to encrypt the backups, and which
folders to include or exclude (again, removing Downloads is probably a
good idea). Note the preferences selection is a separate program to
the main one.

Déjà Dup also makes it easy to set up a schedule and, conveniently,
how long backups should be kept ranging from a week to indefinitely.

Under the hood Déjà Dup makes use of duplicity, which is a
command-line based backup tool for creating encrypted, compressed,
incremental backups based rsync (which, incidentally, you can also use
to make backups but the programs covered here add extra features such
as scheduling).. More info on Déjà Dup.¹

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