Depressed by his decision to reveal his identity to Phin, Miles calles his Uncle Aaron for advice. Aaron suggests a distraction in the form of completing the mixtape he and his brother never finished. Once he collected a sound sample, Miles asks Aaron why he and Jefferson seperated. Aaron then promises to tell Miles the entire story once the latter finishes the mixtape.
Swing over to the docks to begin the mission Aaron (as the Prowler) will give you a USB containing the needed sample. After the cutscene ends, find the hologram with a pre-recorded message, identified by a floating green jumble, to begin the scan. The sound sample needed is a buoy to the left of the warehouse. Holding L2, find the correct volume as getting too close to the buoy will not work. Once in a correct spot, press R3 to record the sound. The mission ends once you find the sample.