As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CAPT O2 MASK RATTLES WHEN BREATHING IN.(<P>SWAPPED CAPTS O2 MASK P/N MC10-08-109 SN SE72273 WITH THE RIGHT SUPERNUMERARY SEAT PN MC 10-08-109 SN B124047. IAW AMM 35-11-51. OPS CHECK NORMAL. REF ITEM 3 THIS PAGE FOR RIGHT SUPERNUMERARY SEAT DEFERRAL.</P>)