Just for clarification when you said gutted the cats do you mean removed it / delete and replaced with a straight pipe?
Try checking the exhaust heat shields under the trunk they do rattle at wot or try test pulling down your exhaust pipe it might be hitting the cross brace bar at the center.
I had to do a washer and nut mod to bring it down( the cross bar) or clamp your exhaust at the rubber exhaust hangers to pull the exhaust up.
That was the case about mine. I only hear a rattling sound at that rev 3000 up.
Now it gone. Btw I placed a dynamat on my heat shields.
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