Azariah Pinney, a man of truly ill-repute by most stories, travelled from England to the West Indies (AKA the Carribean) in 1685. Some stories hold that he was banished, others that he had business dealings. Regardless, on his return he brought with him a slave, a man of African-descent who was poorly treated by Pinney. Pinney died and passed the estates on to his son and, after a time, the slave began to die - whether from the effects of his mis-treatment or a disease contracted in England is unknown - and he stated that he wished for his body to be returned to the Caribean for burial.
Unsurprisingly, Pinney refused the cost of returning the body, and instead buried him Bettiscombe churchyard. Shortly afterwards the house became the center of stramge moands and screams, and objects moving of their own accord. After a while, the body was disintered and brought into the house while Pinney tried ot figure out what to do with it. As soon as the body entered the house, the frightening activity ceased. The soft tissue eventually deocmposed, and over time the bones became lost until only the skull remained.
Since then, many attempts have been made to be rid of the skull. One owner of house threw the skull in a pond, only to have the haunting start up again - it didn't take long for the unfortunate man to pull the skull out of the pond and return it to the house. On another occasion another owner dug a deep pit and buried the skull at the bottom, only to walk out the next morning and find the skull sitting on the ground on top of the now filled-in hole.
Commentary: The screaming skull phenomenon seems to be a type of gohst story unique to England, which is rather odd when you think about it. There are many screaming skull stories (many of which will no doubt eventually show up on this site), but most of them seem to have a few things in common: the skull is associated with an impressive house or similar building, some form of non-aural haunting occurs (poltergeist activity, horrific storms, apparitions, etc.), the skull must be kept inside of the house or some misfortune will occur, most of the stories date to the 16th or 17th centuries, and there is usually a connection to nobility (the skull belongs to a noble person, their servant, or their victim). Interestingly, despite the name of the story (the screaming skulls) not all skulls scream in these stories.
Every source that I have found states that the Bettiscombe skull was examined by archaeologistsa and determined to be a few thousand years old and female, and therefore not the skull of a 17th-century slave.
The concept of keeping the skull in a house will strike most of us as morbid, grisly, or disgusting. However, it should be noted that this has not always been the view. At least since humans began to settle in permanent villages and towns, interring the dead in our places of residence, whether in an attached cemetery, under the home, or within a receptacle in the home, has been a common, though by no means universal, practice. In more recent times, skulls have been kept as trophies - a peice of Californian folkore holds that the severed head of the bandit Joaquin Murietta was kept in a jar in a saloon for decades after he was killed by lawmen, and the posession by American GIs of skulls taken from Japanese dead during WWII was common enough, acoording to forensic anthropologist Dr. William Maples' memoirs.
During the 19th and early 20th century, a variation on this type of practice was seen in death masks - casts of the faces of recently dead friends and family members used as decoration in people's homes.
Whether this practice is the source fo the screaming skull legends or not, I can not say. But it may at least explain why people of the 16th and 17th centuries didn't find it too odd to have a skull hanging around the house.
Sources: Internet, Mysterious Britain, Real British Ghosts, Internet