I wonder if switching it on manually is the same as the car doing it itself. As in, does it heat the engine water when the car switches it on and when switched on manually it only heats the cabin?? So a pump or pulley would not make the noise when switched on manually? Just a thought.. Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

Had a formal diagnosis of a slightly noisy FBH........... although nobody can explain why it is noisy for a few seconds, then quiet, and then noisy again a while later.

While they were at it however they have also diagnosed a faulty EGR valve on Bank A, and a software update required for the powertrain. 2011 Stornaway Grey 5.0SC Autobiography

i suppose you could think of the fbh as a mini boiler so it fires up several times to keep the temperature constant... ... - .- -.




Y. O. L. O.
.

got some time today to have another look at this .
started the moderately warmed up car.
put up the suspension.
every time it made this intermittent noise there was a puff of smoke form the FBH..
so thats it then... 2011 4.4 TdV8 Nara Bronze

Additional Heating
On Td6 models, additional heating reduces the heater warm-up time and is also used to maintain heater performance throughout the drive cycle. On V8 models, additional heating is only used to reduce the heater warm-up time at the beginning of the drive cycle, and only occurs if parked heating is already active when the engine starts.

The ATC ECU activates the additional heating mode when the engine is running and the following conditions coexist:

The ambient temperature is less than 5 °C (41 °F)
The engine coolant temperature is less than 75 °C (167 °F)
The heater coolant temperature is less than 75 °C (167 °F)
The reference temperature is 100%
The blower is on

from the wiki....

Just a thought, it is probably the pump in the FBH which is noisy, it may be a bit cagged up. There is nothing that can't be fixed with a hammer😜😜
FFRR 4.4 SDV8 Autobiography Santorini Black.
KIA E-Niro 4+
2021 Discovery 5 D300 MHEV commercial

The LR Assistance guy.... Second time around as more EGR valve warnings, thinks mine is excessivly noisy inside the cabin, but not partcularly bad on the outside. Maybe some trim of vibration is causing my problem. 2011 Stornaway Grey 5.0SC Autobiography