I have the new 13"MBP and I'm using the Apple earbuds that came with my new iPod Touch. When listening to iTunes I have to turn up the volume at least 75% on the Mac before it becomes unbearable. I have 2 pairs that work the same way. Everyone has a different comfort level in terms of hearing but if you say it's really loud at around 2 bars then your earbuds may be defective. Do you have any other headphones you can try? It shouldn't be that loud at such low settings.
Also, how is it when using your iPod? It should be about the same, if not then something else is wrong here.