I Have both Axis and FMJ's in 400 cut to 27" and I shoot pretty well with them. (07 Alligence #70 29"draw) They are quiet with Blazers but make excessive noise with feathers. Last week I tried some 340 FMJ's cut to 28" with feathers....no noise and they also shoot very well. I haven't had a chance to chrono the different arrows. Do you think it's speed causing the noise or am I close to the spine limit for my set up? BTW I currently shoot 100 grn heads. Thanks.

Most likely a little of both, but I'd lean more toward spine. Could be the 400's just weren't straightening out that well and those feathers had to do more work. Stands to reason if they have to catch more air they're going to make more noise.