Snake ID

Unfortunately I do not have any pics as of yet. My brother saw the snake in our yard (forced over here because all of the water I suppose). I walked out to confirm if poisonous and kill if necessary, and I could hear the snake rattling in the bed. After grabbing my snake murdering apparatus said snake was nowhere to be found. He did not leave the flowerbed and I dug around in there for 30 minutes and could not find him. According to my brother the snake was black, 4 foot long, and rattling. This does not sound like a rattlesnake to me, nor have I ever seen one around here. However I did hear him rattling pretty clearly. Do rattlers ever appear black? Please advise.