Drive train vibration. Scratching my head.

You did not say who's gear set you used.
After market gears are not like they used to be, some are noisier than others.
Point is good luck finding a current after market gear set that does not make some kind of weird noise. Even with a perfect pattern.
I believe it's Motive gear set. No gear noise. It's the vibration that is causing the noise and only at high speed/RPM. Very faint at low speed (35).