As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT FOR TAKEOFF VERY LOUD AIR RUSHING SOUND AFTER ADVANCING #1 THRUST LEVER PAST 25% N1. ALL C/B'S CHECKED IN. GROUNDED - YES. REMOVED AND REPLACED L/H FLOW CONTROL AND SHUTOFF VALVE IN REF TO B737-800 AMM 21-51-01. RAN ENGINES WITH NO ABNORMAL NOISES.