I have a Mk1 and as I have said elsewhere on this forum, at speed the greatest noise in wind noise. Followed by tyre noise and then engine noise.
I regularly check my window are up, as my wife is always opening hers a bit. The window in the back of my "cooncil" model are windy up ones, and sometimes they relax a bit, which doesn't help wind noise. As Vic says, they don't have to be actually "open", just not full closed.