Eh? The sound from the device is great, try using a better pair of headphones. There is a sound equaliser, under settings - iPod - eq.
If your talking about sound coming out of the devices speaker then try turning the volume down a bit on whatever it is your playing. It's s tiny little speaker, if your blasting some shite hip hop through it then it will probably go all distorted yes.
That's the iPhone 4 telling you you have poor taste in music though.
I hope that helps.