How can I remove the loud BEEEEEEEERP noise the doors make when they open. It sounds like a prison cell has been opened and i don't really want that in my map.

in mapname.gsc is a line that includes the sounds just remove it

When you only want to remove it for certain doors, give them an invalid script_sound (as KVP).
you can also change the sound that way (if you enter a valid one).