It is generally agreed that Davis began to lose his voice in the early 1970s, around the same time that he began to experience respiratory problems. These problems may have been caused by a combination of factors, including smoking, drug use, and exposure to loud noise. Davis was also diagnosed with laryngeal cancer in the late 1970s, which may have further contributed to the loss of his voice. Whatever the cause, Davis's voice gradually deteriorated over the years, and by the time of his death in 1991, he was unable to speak above a whisper.