It's a cultural thing derived from the Southern United States. Coined "Black Rednecks". They simply copy the English, Scottish highland people who lived in the hills of the UK back in the day. The real Rednecks from the present day UK came over with no manners, quick to react without thinking behaviour, etc.... The black slaves in the south simply copied them since they were within close proximity... The blacks just never let go of the behaviour. Look at the Baptism religion, very loud, singing, shouting the sermon, etc. Then the blacks moved to different U.S. Cities and simply repeated the behaviour. Very weird and Interesting. Africans I know in the States think that Black people are not liek they are. Black people in Canada are like white people in Canada, the Somalian gangs notwithstanding.
Because Black people of the US ARE different than Africans---sheez.
Most Africans Who come to the US are pure bred, and Black Americans are mixed, they even have words for us---and look down upon the fact they we are not "pure" like them.
Culturally we are an amalgam of Euro, W. African and a little bit of American Indian (depending on where).
As far as the loud talking, my folks are from the south, and they don't talk loud. But, it could be a cultural thing, as I know people Down south who like to laugh real loud