Tall barbs without good support make noise.
I had some "trad/P&Y" feathers that were real hissers.
Went from this cut...
to this cut...
I just cut the backs off about 1/2 height at a 90˚ angle.
Helped a LOT but having those unsupported barbs in the back still made some noise...just not near as much.
That's why naners are so quiet...the tallest barbs have a lot of support from the shorter ones.
I've found what I feel is a "sweet spot" with the t-hawk shape by lil-chopper.
not a naner but not a parabolic...
Good luck to you.