Once extracted, you typically find a file like Bach_Guitar.mp3 or a .jpg of sheet music.
Use strings to look for readable text at the end of the file. Inspect the LSB (Least Significant Bit) using zsteg . Open the file in Audacity .
Text appearing as "waves" in the audio spectrum.
Check for DTMF tones (phone keypad sounds) that might represent a code. The flag is usually hidden in one of three ways:
Brute-forcing if the hint suggests a simple word (like "bach" or "guitar").