WRX_MIKE_WRX

I have been experiencing a rattle that occurs at around 3k revs and also 5k. I took it to my local garage who said that the centre cat had gone and this was the cause. I have now just replaced this with a de-cat (the cat was gone sounded like a rain maker!)but then i took her for a spin and its still there. I cannot locate where this is coming from but I would say its from the engine bay, lower front drivers side there is a metal heat shield running all across the front what i assume is the manifold maybe that?. Anyone else think what this could be?

ProdriveSTI

What kind of rattle sound does it make?
Does it happen on tick over?
Or when reved?

I had a rattle/vibration when I floored it betwen 3-5k, it went when past 6k rpm tho....