Draught through cooker hood

I am in a new-build house and am having issues with a strong draught through my cooker hood, which makes the kitchen cold.

The hood vents to outside, through two permanently open air bricks in the wall. I can't see how the hood is ducted or connected to the air bricks, though I assume it is.

What could I do to stop the draught? I have looked at cowls to shield the air bricks, which may help, or I wondered about some kind of gravity grille over the bricks (but then I'd need to see how the hood is ducted to the bricks, to ensure the bricks only service the hood and not the wall cavity).

Any guidance greatly appreciated.