rap out
1. To create a rhythm by tapping, knocking, or lightly striking something. A noun or pronoun can be used between "rap" and "out." He rapped out the secret sequence that allowed him to enter the hideout. She rapped a beat out for me while I freestyled on the bus.
2. To utter a particular message or line in or as a rap performance. A noun or pronoun can be used between "rap" and "out." He rapped out a few lines about his life in Detroit and the oppression he felt from the police. I find that rapping my problems out can be pretty therapeutic.
rap something out (on something)
to tap out the rhythm of something on something. Try to rap the rhythm out on the table. He rapped out the rhythm on the table.