The '74 Nova 250 6 cylinder that I had with the 1 Barrel Monojet also whistled under certain conditions. I could usually make it do it when I messed with the idle mixture. Certain speeds and mixture combintations led to the whistle. I just richened it a tad to eliminate it . I cannot remember if you could hear the whistle with the air cleaneri installed, but definintly without it! Great car, great engine- very reliable and smooth.
