The silver 540 had started making a "bearing" type noise seemingly coming from alternator (?) area. The alternator was also producing a bit of a whine on the radio and new bluebus (more so on bluebus), so a spare alternator was procured and I set about taking it all apart. However I noticed the water pump was very "grindy" sounding when the belt came off. So taking the WP out and strangely it turned OK when out of the car. Then I found the reason... the bolt internal to the WP holding the cover had come loose and was machining itself on the impeller...
A bit of a cleanup, some loctite, a new gasket, changed the alternator anyway, and all is well again. The noise on the bluebus is much reduced, but still there...