I've got a 2009 Impreza RX and at around 2100 - 2200 RPM there is a rattle which resonates from around the engine/gearbox area. It only happens in that rev range and only under light acceleration or deceleration. If I put the boot in I don't hear it. My gut feeling is it's a rattle coming from the exhaust somewhere, it's reaching some point of resonation and that's causing the rattle. I've crawled under the car and can't find anything loose with the exhaust. It doesn't seem to have any other impact, it's not very loud but I notice it and it's annoying. Any thoughts people? I'm wondering if it's a common problem?