RE: How much louder are feathers???
Rather than making this a book, I'll just list some criteria.
1)Feathers have a larger drag coefficient, so control of BH's will be better if the same 'contour' is used.
2)Feathers will increase noise as a)speed increases and b)angle/helical increases.
3)Feathers can have less penetration (all other things being equal) than vanes due to the increase of arrow weight with vanes; however, the difference would be very minor.
4)Damaged feathers will not exhibit as much noise as damaged vanes with certain exceptions.
5)There is one new vane on the market that is very noisey in flight. I think it is presently being redesigned after my test report back to the manufacturer.
Hope this helps.