How do u know when ur drums are bad on ur '99 F-150?

my rear brakes has a rumble when I brake could it be the Drums Cause I changed the shoes my self but I didn't pay any attention to the drumsHow do u know when ur drums are bad on ur '99 F-150?Did you turn the drums? If not, turn them.
How do u know when ur drums are bad on ur '99 F-150?
grooves worn into the drum or uneven wear on your brake shoes