Possible Clues:

• Coolio and Ice-T, e.g.
• Q-Tip and Ice-T
• Eric B, Pimp C and Chuck D
• Rick Ross, Roddy Ricch and Rakim
• Singers' covers on the radio
• Eminem and Jay-Z, say
• Jay Z and Dr. Dre
• '___ Delight,' pioneering song by the Sugarhill Gang
• Musicians? They may be knocking at people's doors
• Dr. Dre and Eminem