As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOUD WHISTLING NOISE WRT RECIRC OR BOTH PACKS ON. AIR NOISE TOO LOUD INTERF W COCKPIT COM. COMPLIED WITH MEL. CK SOUND & AIRFLOW LEVELS AT START & END TO COMPARE IMPROVEMENT. SUGGEST ACP STEP-4 OF ABOVE SVC TIP. IF NO FAULTS FOUND SUGGEST REPLACE LT PACK FLOW CONTROL & S-O VLV. ADDITIONALLY CHECK CONN AT L PACK TEMP VLV. REPLACED LEFT PACK FLOW CONTROL & S-O VLV PER MM, OPS CHECK OK.