Well, its kinda complicated. The easy answer is its just years of strain. Working so much, plus in venus where smoking was the norm, took its toll. Also remember after Elvis dies, Newton took on the role as Mr. Las Vegas which meant taking over Elvis' old digs at the LV Hilton, performing two shows a night, 6 or 7 nights a week, for 7 years straight. Part of it may be his style of singing as well; never taking lessons, he may have been singing "wrong" all these years to where he has just flat-out worn out his vocal chords. This may have been the price he has paid for singing so well for so many years in his distintive voice. As Newton has said himself, even Sinatra wasn't singing the same way later in life. Lastly, the man suffered from aesthma and respitory issues. Combine all of this and