We've had a few folks that are dubious about the amount of noise that can come from the headers and question the need to wrap the headers.
I'd like to share a little story of my own from a few years back that may help some of you understand why we are asking for this.
It was on my old Honda CBX. As it came to me there was an old Macs full exhaust system on it. This thing was NOISY! It also hung down like a broken wing and I found myself dragging the headers a couple of times.
The old stock pipes had come along with the deal so I cut off the very rusty mufflers and made up an adapter so I could use the stock headers with the Macs mufflers. The Macs headers were single layer tubing with a very thin wall. The stock Honda headers were a double wall design to help keep the chrome from blueing.
Even with NO change to the noisy muffler I was amazed at how much quieter the header swap was. Just adding the second tubing layer to the headers reduced the noise by a dramatic amount. Now I know the stock headers also were more restrictive but frankly I didn't notice a big change coming out the tail until I did some mods to tha actual muffler. The noise that went away was the sharp metallic ringing sound that apparently was coming through the thin wall headers. Best of all is that the noise that was close to being painful up close when revved was reduced to where it was just annoying.
Yes this IS highly UNscientific but it does point out that the thin metal of many headers lets through a surprising amount of sound energy. Adding the header wrap can only help to damp this noise.