2008 BMW 750Li E66 suspected bearing noise

2008 BMW 750Li 90K km year base oil change and coolant radiator drain and fill three years ago at 70K km, no coolant leaks.
A year back a suspected noise can be heard when hood open while engine running, the noise doesn't develop as time goes by.
Further inspection will be taken by stethoscope or serpentine belt removed when I get time.
It seams that tensioner pulley or water pump on its way out. but alternator or compressor bearing may suspected too.
Similar noise: • BMW Failing Water Pump... [noise from 0:32 to end]