I had a hum at one point in a 500 I owned so I removed the ground screw and it went away. No, you don't have to leave the screw in place for the sub to work. Normally you don't want to remove the screw, and address the hum in other ways.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85