As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT WAS INFORMED BY LINE PERSONNEL DURING TAXI TO TIE DOWN, THAT ENGINE WAS MAKING A LOUD (AIR PULSING) SOUND. PILOT COULD ONLY HEAR THE SOUND AFTER REMOVING NOISE CANCELLING HEAD SET. PILOT THEN SHUTDOWN ENGINE. INSPECTION REVEALED THE NR 4 CYLINDER TO BE CRACKED AT THE PARTING SURFACE. EXHAUST WAS ESCAPING FROM THE CRACK CAUSING THE (AIR PULSING) SOUND.