What the heck, never had this happened to me before.  Well the occasional one has done it, but now it seems like every other shot whisles.  My feathers are new too?  Mabye they just need to be worn in a bit?  Any thoughts?

what kind of cut are you shooting? I have had some loud feathers with traditional cut & sheild cut at 5 1/2 in.

The loudness of the feather is usually contributed to the height of the feather of the shaft.  High back sheild 5.5 high profile bananas trads and p&y are the worst that I have noticed.  Are they field points or broadheads.

The 5 1/2" high backs will whistle. Take a pair of sissors and trim one down so the highest point from the shaft is about 5/8th high. Depending on the feather, some batches are more softer then others and as a result the top of the feather bends over in flite allowing it to whistle.

Well they are 4" sheild cuts?  Feild tips, and actually it could be my new brass inserts, now that I think of it.  They have a tiny, tiny lip when the feild point is on there, but not when the broadhead or judo is on there!  Actually no it cant be, some were doing it before that!  I think it could just be the weather or something, they just started doing it today, I noticed it slightly before I put in the brass inserts, but didnt think much of it?

I use a high back 5 1/2 Bannana cut-- and wind up with a few whistlers in batch of 12.  I like em--sounds like the arrows in the old Indian/cowboy movies/ or original Robin Hood w/ Erroll Flynn and H.H.  When I want to quiet a whistler I just clip the rear !/2".  As far as target shooting goes, or 3D I'd just a soon they all be Whistlers-- just adds something to the esthetic of the whole thang.