What was found
AIRCRAFT WAS GROUNDED: PRONOUNCED LOW FREQUENCY RUMBLE FELT THROUGH FLOOR DURING HIGH ALT CRUISE, FL330-380 ..75-.79 IMN, BEGINS AT 81% N1 TO 84% N1. BELOW AND ABOVE 81-84% NO RUMBLE. ALL ENG IND NORMAL, N1S EQUAL.N1 VIB NBR1 ENG 0.2 / NBR2 ENG 0.9. N2 VIB NBR1 ENG 0.2 NBR 2ENG 0.8. VIBRATION READINGS STEADY ALL THRUST SETTINGS. SUSPECT RUMBLE IS AIR DUCT HARMONIC, WHICH MAY BE CAUSING ON GOING AIR BLEED CLASS II STATUS AND ECAM MSGS. DECESION MADE TO RETURN TO PHX, EMERGENCY DECLARED LANDED OVERWEIGHT WITHOUT INCIDENT. MAINTENANCE REPLACED REPLACED #2 ENG PRV IN REF TO MM 36-11-52.