Xantia 90Hdi. Really frustrating noise; any ideas?

[VertVega]

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Second option could it be the small fan of the cabin temperature sensor which is next to the clock, behind the small grill. Some air pressure would clean it.
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This was what I was suggesting then. The fan is as big as 1 euro coin and might sound like a fly

[DickieG]

DickieG, where is this? Is it in the temperature sensor window in the centre of dashboard?

Yes right at the far left end of the band running across the centre of the dash, apologies I forgot that with yours being a S2 the alarm LED is by the O/S mirror.

[DickieG]

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Second option could it be the small fan of the cabin temperature sensor which is next to the clock, behind the small grill. Some air pressure would clean it.
...

This was what I was suggesting then. The fan is as big as 1 euro coin and might sound like a fly

Apologies for my repeated post, I missed your earlier suggestion

[VertVega]

No problem at all I was admiring our timing at clicking the Submit button at the same second

I have once gave some pressurized air there. Not full power!! The noise was like (don't laugh) a fly behind the window
which is trying to get out and hitting the glass every now then.
Sorry I couldn't find a better way to describe it