DannR,
The road noise is exactly that; nothing related to the format of the music. Imagine you are riding in your car with the radio/music player turned off. That "noise baseline" of the tires, wind, and engine requires that I turn up the volume (compared to if the car isn't moving and all can hear is the radio/music player).
If I convert to MP3 with Switch (or any other decent app) and listen to the music on my desktop computer, the quality is excellent. It's just when you introduce the "noise baseline" of riding in a moving car that I have to turn up the volume in order to hear the soft spots (and that's what gets the loud spots "too loud"). The music itself has no noise.