That noise I hear at around 3200-3400 rpm is GONE!! I removed the heat shield this weekend when I was changing my oil. No more noise. My car sounds so nice when revving up through the gears. I know many of you have this same problem, so if you want to fix it, remove that shield.

 

I thought that was a bad idea, generally? I've been told you can easily turn leaves, paper, plastic, oil, gas(!) anything flammable under your car, into a flaming inferno in a matter of seconds without the cat heat shield in place.
Maybe that's an exageration, but it's pretty much what I've been told.
By the way, I have that noise too. My mech said not to worry about it. But it is annoying...

 

If that were true, then, there would be fires everywhere. the Cat isn't the only part of the exhaust that gets to that temperature. The entire exhaust is that hot, but, yet, when people swap out the piping, they take off whatever shield that's around them. And, there car doesn't start on fire. I wouldn't worry about it if I were you. Plenty of people have done this, and, have had no problems. So far, my car is still in one piece.