[wuli]

I always have weird sound when driving on uneven road, the sound seems from the chassis, but only hear that when driving on uneven road.
I have checked all my items in my car. I took that out, and still hear that sound.
I ask my friend who seats in the passenger seat try to find where is the sound
from. He said that is from middle of car, not from the chassis.
Description of sound: It is like 2 metal materials collide with each other. I can hear the sound when no radio on, that's mean the sound is not loud.

First question: Does any thing put in the truck cause any sound like from chassis?
Second question: How can I figure out where exactly weird sound from?