What was found
ON INBOUND FLIGHT ON T/O F/A'S NOTICED AN UNKNOWN ODOR FROM THE AFT OF ACFT THRU FWD OF ACFT INCLUDING FLT DECK, DISSIPATED DURING CRUISE, THEN ODOR APPEARED AGAIN ON DESCENT. RAN ENGINES 1 AND 2 AND APU NO ODOR NOTED. PERFORMED AMM 12-33-21-618-801-402. PRECONDITIONING CHECK, NO FAULTS NOTED. OPS CHECKED GOOD. OK TO CONTINUE.