While you are at it, check the heat shields for hairline cracks at the mounting holes. I was having the same issue with the noise in the same RPM range as you. I went through pretty much the same steps as you are, but it still did not fix it.
Then I took the shields off and did a very close visual inspection and found hairline cracks on both Ti shields where they fasten to the pipe. While they were off, I decided I liked the look without the shields and did not put them back on.
2003 Honda 919, Carbon Sato's, PCIII-USB planned asphalt gray
2007 Majestic Blue NISMO KC, 4x4, 6-speed, Gibson catback, Clarion DUZ385SAT
2007 Trek EX8-Custom parts build by me for me
1992 Nissan 240sx- SR20DET swap, HKS intake, exhaust, and SSQV, VLSD, S14 Silvia JDM seats(super comfy), Exedy clutch