Your grandfather probably was referring to a lot of jabbering or meaningless talk when he mentioned chin music. The term is pretty creative, because it relates the human anatomy to an instrument. Of course, not all music is beautiful!
In Stephen Crane's The Red Badge of Courage, a novel set during the U.S. Civil War, a "savage-minded lieutenant" vents his dissatisfaction:
"There's too much chin music an' too little fightin' in this war, anyhow," he said to them, turning his head for a final remark.