Thinking out loud here...
When I installed the cat pipes, I did not loosen or remove the mufflers. The AWE cat pipes lined up nicely in the cat-to-muffler sleeves without issue so it never occurred to me to mess with the mufflers. The sleeves didn't slide loosely, but in my experience with these sleeves, they bind a bit with wear and corrosion anyhow so I didn't think much of it.
Is it possible that even though they lined up nicely during the install, they are at a slight angle with the mufflers that is allowing a leak there at the sleeve at 3K and upwards, but not at idle? At idle, there is zero leak, but I have not tested for leaks under the car with someone holding revs at 2,500 for instance. Cold is the best time to test, letting the car sit overnight. This way you can wrap your hands around the seams before they are too hot to touch and have someone else start the car. Typically, even the smallest leak with be immediately noticeable so no leaks at idle should mean no leaks whilst driving...
I'm grasping here, but I'm eager for it to be something small that I can fix. I imagine the solution would be to loosen everything, including the mufflers this time, and tighten down the chain (from header to tip) to allow for better alignment. There are no gaps at that sleeve that I can see, but who knows...if the sleeve is off by a few degrees, perhaps it's allowing exhaust to blow past once it reaches a certain volume (3K rpm). This may also explain why it's sounding a little less crazy with some heat after 10~15 minutes due to expansion there.
Anyone else been through this? I may just be off my rocker...but I figure it's easy enough to try. It also makes me wonder if this is why rasp and odd sounds seem to vanish when folks install mufflers after just doing cats. It's not necessarily that the new cans have fixed it, rather the proper re-alignment of joints that takes place when you put the new mufflers on.
