My 04 ep3 type r facelift has an annoying rattle coming from underneath the car towards the front, the rattle is at 2500 rpm and comes and goes seems to be louder when cold, have removed the driveshaft heat shield and did not make a difference car has a cat back system fitted any ideas as to what this noise is ?

 

Check tensioner and chain

 

I just recently purchased a EP3 from Japan and had a similar rattle at certain revs, I figured out that my exhaust silencer was moving around since it was fairly long and was only held in by one Allen key bolt. I put a couple layers of electrical tape so it fit more snug.
Not sure if your issue is similar, but when I first heard the rattle I thought mine was my heat shield at the front. It was hard to pinpoint where the sound came from, that's all.