Rattle during acceleration
 

For a few months now I've been hearing a metallic rattling sound when pressing the throttle, even if lightly pressed when coasting at constant speed. Sounds like something loose flapping around and it's coming from under the hood near drivers seat. Rattle can start anywhere around 1500rpm and goes away as revs or boost increases, usually around past 3 or 4000rpm. Otherwise when I back off the throttle it stops instantly. Rattle can even be heard if I press throttle to rev the engine when out of gear in neutral, so it doesn't seem to be the transmission. Does anyone know what it may be? I have a stock 2003 evo viii 127,000km.

Easy to check but that is the mileage (kilometerage?) where the stock exhaust heat shields rust through and fall off.

What fuel do you run it on?

well, just check for lose stuff,
would be easier if u got someone to rev while u observe where it's coming from.

check the downpipe rubbing on the underbraces

Can also be spark knock,ping,detonation. Can verify or elminate the possibility by logging knock sensor activity.

Thanks all for the suggestions. I run premium 98 octane. Will try a few things and let you know.