When I run the following command:
dd if=/dev/sda of=output bs=512 count=1
In the middle of the output, I see this text:
GRUB ^@Geom^@Hard Disk^@Read^@ Error^M
What does it mean?
Those are just strings that GRUB has in its bootloader. This doesn't mean that you have a hard disk read error, just that GRUB has some text in its bootloader that will be displayed if you do.