Three years ago we purchased a 30+ year-old, custom-built home. Last month we replaced the windows - with 'unbalanced-pane' windows. These unbalance windows have a 2mm pane of glass on the exterior-side and a 3 mm pane of glass on the interior-side.
Our home is MUCH QUIETER now. Unfortunately, new windows cost as much as a high-end component (or even system). Still, if you need or want to have new windows installed, they can significantly reduce the ambient-noise floor. I hope the 'unbalanced pane' tip is helpful to those considering a renovation.