Massimiliano Antonio "Max" Cavalera played keyboards in the band Soulfly not the artist Gwen Stefani drew inspiration from in her song 4 in the Morning.
Massimiliano Antonio "Max" Cavalera (] , born August 4, 1969) is a Brazilian singer, guitarist, and songwriter who currently plays in heavy metal bands Soulfly, Cavalera Conspiracy, and Killer Be Killed. 
William Michael Albert Broad (born 30 November 1955), known professionally as Billy Idol, is an English musician, singer, songwriter, and actor. 
 Described as one of her favorite songs on the album, Stefani began writing the song while pregnant and finished with Kanal, drawing inspiration from Roberta Flack and Billy Idol. 
