The Sound of Sound from the Vehicle

There is an interesting voice in my car that I noticed the other day. It is heard more when the vehicle stops. A subtle sound, as if metal pieces hit each other. When I leave the car when I idle where I can hardly hear it, the sound stops when I give it some gas. It starts again when you release the gas. It is gnawing for 2 days to see if there is a cost again. I hit the car recently, but it's not a very hard hit. I wonder if it was from him. Anyone have an idea about this or what happened to you? I looked on the internet a little valve adjustment, in most places. I'll be happy if you can help me.

Thanks in advance ..