What is the grinding noise?

I hear a metallic grinding noise when gas pedal hits certain spot. What is it?

• I drive a 2008 Scion xD automatic. My car recently started making a metallic grinding noise when the gas pedal gets to a certain spot. I just took the car to the dealership for an oil change, and had them drive the car around. Of course, they found nothing. The noise sounds like brakes do when they badly need to be replaced - that metallic grinding screeching noise. The noise is very noticeable when the engine is cold. Once the car has been fully warmed up the sound is hard to replicate. However, I found today when driving on a flat part of the highway I was keeping the car steady at 60mph and the sound was constant. I was thinking it might be a loose heat shield somewhere. The car has to be in motion for the sound to occur. It doesn't happen when the car is parked and I rev the engine. Doesn't happen when I turn the car either. This only happens when I accelerate. The two speeds it tends to happen at the most are 40 and 60mpg, but those are the speeds I tend to cruise at the most, so I guess it's safe to say the gas pedal is constantly at that spot. I'm hoping someone can give me some clue as to what the problem is. I can hear the noise when the windows are rolled up and the radio is on low, and when the windows are down. It sounds like it's coming from the front, but since my car is so small it could be from anywhere.

• Answer:

  look at your exaughst covers like the one covering your cat converter ..... loose vibrating...... happened to me