the noise at 1400 rpm is getting worse. it happens whether moving or idling. the window for it is really narrow- you have to be right on the (not so)sweet spot right around 1400 rpm and there is suddeny this metallic rattling noise. i'm not sure where it's coming from- unfortunately i don't have anyone to step on the pedal right now so i can figure it out...

could it be the catylitic converter?