As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER 3.7 HRS IN ACFT, BLEED VALVE STARTED TO MAKE A HOOTING NOISE AND ALSO PRODUCED VIBRATIONS. ABOVE SYMPTOMS WERE ONLY SEEN ON POWER REDUCTIONS. ORIGINAL BLEED VALVE, WHICH HAD TIME REMAINING ON IT WAS REINSTALLED AND THE PROBLEM WAS RESOVLED.