MuskUp

I had this issue and it drove me nuts, didn't matter what setting it was on and went away when fan off. Thought it was seals too. Ended up taking it in for help and dealer used pressure sensor and found it was actually caused by faulty trim in the boot. Padding/deadening had fallen away covering vent (presumably intended as pressure exit) and it just manifested as irritating sound of air escaping next to my flipping ear. Trim replacement under warranty sorted it for me if yours is similar.

Just here to add thanks. Great write up/parts list etc. Just done this afternoon and all works a charm and went as described.

Thanks both, yes the GT85 through the grommet was great help and all the rest was fine but getting from that D-pillar into the headlining cleanly beyond me for some reason. In then I fed through the bodywork and pulled out into headlining through a gap just above the rear passenger door. Not ideal but does the job and thanks to these great guides and info it's working. I'll maybe re-route when I can face it as working around the curtain airbags also a pain. Much rather have it but I find it takes some getting used to as it's a really aggressive fish-eye lens on there (can't be that my parking is rubbish).

Still playing with this as who needs skin on their knuckles anyway? Anyone skipped headliner/piggybacking on internal looms and gone straight through bodywork frame to the A pillar? Bit concerned about taking wiring that way as never done it previously but seems I can achieve that whereas this route I've started from back to front is defeating me as above?

Any tips (Mark III Estate) for getting the wiring from the D pillar grommet entry to join up with the headlining over rear passenger door please? Just picked up my Octavia couple of weeks ago and wanted to follow the excellent guides here and advice from @SashaGrace by wiring up through headlining (but inside/above the airbags). I'm going spare trying to get a fish/net curtain rod/wire coat hanger/any flipping thing from that D pillar entry into the car there. Seems to have been simple for most others so just wondering if anything mark/model specific to know. Rest of wiring looks to head down to the floor. Thanks (and thanks for the great guides/advice all over here.