Just curious as to what these little flaps are for to the rear of the spare wheel well. Look like a cat flap for a very small cat. Presumably to let air out but not back in again when the heater blower is on? But why in the boot & how does it get from the cabin into the boot or am I missing something obvious?
They’re a very common feature on most cars, hidden so you won’t notice them and behind panels so you won’t block them.
They help to keep the car dry by guaranteeing an air flow through it.
The openings are intended to be at low-pressure points and also clear of mud from the wheels.
No2 Son has theses in his Golf boot and were stuck open allowing water/road spray into the boot.
The key word I used was “intended”.
Allegedly introduced by Ford in the Cortina as the airoflow system.
If the air can’t get out, it can’t flow.
If these can and do get stuck, maybe they are contributing to the road noise from the drains/noise ducts?
I’m pretty sure they are to let the air out when you close a door, and when you have fans in high but windows closed, somewhere for the air to go.
Good point about how does the air get from the cabin to the boot?
Maybe they are to reliever pressure when shutting the boot lid?
They are also useful for enduring your boot never gets more than half full of water which would upset the handling 
Hmm, I recently put some Silent Coat in strategic spots on the back of all four boot trim panels. It has made a big difference to the noise levels in the cabin. Maybe some noise was coming from those flaps!
I know they were shut when at rest and fiddling in the boot, but if the air is passing through, then they open and as the air goes out the noise comes in!
I’ll add some of the sound soak-up facing and around each vent as well to stop the sound bouncing around. I have a few bits left over from a bigger job.
Air escape for inside of car and don’t forget your fuel tank is in the boot, so helps dispel any fumes.
Could this be the answer to why the road noise is sooooo much worse with the lid up?
If the lid is down, the ventilation air is escaping to atmosphere and the flaps perhaps remaining closed,
With lid up, the air can only escape through the flaps, allowing the road noise through…
??
So you applied it to the back of rhe trim panels, rather then the metal??
I did the metal a couple of years ago and it made a big difference, but was not a complete solution. So this was extra to that.
In an idle moment with coffee in hand while admiring my work sorting out the sound quality (curing unwanted panel resonances in an otherwise excellent design) of a PA speaker I finally read the Silent Coat instructions!
In the paperwork that comes with Silent Coat it mentions trim-panel resonances, and sure enough if you tap the panels they are quite noisy, especially in the annoying upper frequencies.
Adding a bit of mass to some areas, and it does not need to be everywhere just the wider un-braced bits, drops the frequencies a lot, so now it is no longer similar to tyre or wind noise. I’ll take them off again to add the foamy stuff I mentioned and post some photos later today.
EDIT.
Added some pictures showing patchy and untidy mass-deadening and sound absorbing foamy stuff added to trim etc.
However it does not matter if it is untidy so long as it works and fasteners etc are all accessible. Tidy is more likely to resonate!.
Driver’s side vent
Driver’s side trim
Passenger side vent and wiring clutter (I did remember later to click home again the filler release cable)
Passenger side trim
Too wet to go out today for a test and I’m waiting on a delivery. I don’t envy the poor driver his job.
Ah, that takes me back. Yes, the introduction of airoflow on the Cortina Mk1 (1964?) used very distinct grilles on the C pillars to allow air out. I guess they had some sort of one way flap behind, but never dismantled one to find out.
JS
Went to and from the bank the long way round, via some noisy surfaces; one way top down, one way top up. Now I do not hear much of a difference in the tyre noise, except top down is noisiest especially when bouncing off other cars or walls etc.
I think now when top up the drains are the loudest and not much from the boot area. I should have taken some noise readings, but my other driver is pre-occupied, and does not like the clutch.
While still nowhere near professional standard, this generic little freebie noise meter is better than I expected, and is useful for comparisons, even if not absolute levels.
