I was looking for something and saw that the novel mentions what Monkey sounds like:
And his voice resounded like bells and [stone] chimes (Wu & Yu, 2012, vol. 1, p. 152).
... 聲音響喨如鐘磬。
Since he's a celestial being, it would be interesting if his voice sounded like someone rubbing their fingers around the rims of wine glasses (i.e. glass harp).
Source:
Wu, C., & Yu, A. C. (2012). The Journey to the West (Vols. 1-4) (Rev. ed.). Chicago, Illinois: University of Chicago Press.