Have you ever checked that area in the 7 years you have owned it? Can't say I've seen white powder residue from water ingress so wondering if it's something a previous owner spilt in that area.

Yes, It is normally very clean and dry. To me, it is as if something is fizzing due to a bad connection coupled with damp/water ingress although there is no smell. I have yet to start stripping back the plastic surrounds.
I hasten to add that the water wasn't deep enough to upset the compressor and all else appears to work OK. I last had the covers off a couple of months ago when I carried out internal cleaning Previous cars:
S-Max 2007-2013 (only diesel I've had, good car but expensive when diesely bits go wrong, so what's the point?)
Galaxy 2001-2007
Mondeo Estate 1997-2001
Sierra Estate 1993-1997
Uno Turbo 1987 -1993
Fiesta 1984 - 1987
Fiat 127 1982 - 1984

Panic over. It is cement dust (Doh)! Will keep an eye on the water situation. Previous cars:
S-Max 2007-2013 (only diesel I've had, good car but expensive when diesely bits go wrong, so what's the point?)
Galaxy 2001-2007
Mondeo Estate 1997-2001
Sierra Estate 1993-1997
Uno Turbo 1987 -1993
Fiesta 1984 - 1987
Fiat 127 1982 - 1984

Well I would class that as a result, better it's cement dust than something catastrophic

I had some problem with a lot of water ingress into spare wheel well with the wheel out I could see that water was creeping in from either corner at the front of wheel well it transpired it was the upper tailgate fixings so I plastered them in silicon seems to have cured it. Thses cars are a pain in the arse for leaks!! Range Rover Vogue SE 4.4 SDV8 SVO Stying Pack
Audi A4 2.7 TDI S Line Black Edition phantomn black
Previous Cars
Range Rover Vogue SE Overfinch Styling 22" Elara's full black stealth colour coded
Java black Range Rover sport 2.7 TDV6
Alaska white Range Rover sport overfinch 3.6 TDV8
BMW M3 Carbon Black

I had an issue with the vehicle forever misting up. 1" water found in wheel well. One 3mm hole later and done! Cheers

James