HEy Agd,
I have a question.....did you glue your fletching down? IF not, the entire feather will flutter and vibrate in flight, resuting in a lot of noise. Gluing the vane of the feather makes everything more rigid in flight, and it helps keep excess noise to a minimum.
Also, turkey tail feathers seem to be much more quiet in flight when compared to the wing feathers. The wing feathers are much thicker and sturdier, but they also have a rougher surface texture which tends to create more turbulence that creates noise. The tail feathers are softer, which helps eliminate noise. As Mechslasher said, some downy feathers tied to the front of the fletches will helps dissipate noise, but don't make them too big or they'll slow your arrow unnecessarily.
IF you have a really radical helix on your fletchings, that can also increase noise. I give my feathers a decent twist, but I don't overdo it. And I ALWAYS glue the fealthers down on my hunting arrows.
If your arrows are well matched to your bow, you can get away with surprisingly low-cut feathers and still get perfect flight. For years I had a cane arrow that was fletched with turkey tail feathers that were only 1/2 an inch high. That arrow flew perfectly everytime I shot it, and I took that arrow hunting with me all over the country, from Iowa to New Mexico to Oregon to Georgia. I killed 2 rabbits with it, missed a deer and then shot it right thru a deer 2 years ago. It was so quiet in flight that the animals never heard it coming. Unfortunately the last deer I shot with it kicked up like a mule and broke the fletch end off inside of her. I still have the forward 2/3 of the arrow, but the rest is in that deer's decaying body since I never found her.
Hope that helps.