That’s a good question when it comes to pollution but man, the constant whine of wheels on a freeway drives me insane.

For me it's the semi-trucks, modified passenger cars/trucks and motorcycles. Normal cars sound more like white noise. I used to live 2 miles from the freeway and could pick out the problem vehicles when there was an inversion layer to reflect the sound back to the ground.

And horns. I fuckin hate horns. I swear car horn noises reach into the far ends if the universe, you can't escape them.