Last night QF9 (Melb-Dubai) was diverted back to Sydney
Qantas A380 in epic overnight diversion | Plane Talking
The reported reason was "QF9 was about three and a half hours into its flight to Dubai from Melbourne when vibrations become apparent in an engine."
Are there "vibration detectors" on each engine of an A380, or is it simply that the flight crew noticed something? I imagine this doesn't happen often - what would cause an engine vibration to get worse in-flight? I'm guessing it wasn't a chunk out of a turbine blade 'cos that would have much more dramatic effects.