sira5012

I have a 2002 Impreza RS and about a year ago it started making a rough, (metal-on-metal?) noise but only when I'm driving at 1750rpms. It's progressively gotten worse. The mechanic thought it was a loose piece of metal or a rock that was rubbing against something. He took the metal and rock out and said it was fine, but the noise is louder!! Any ideas? Please help!