The arrows showing slightly weak might be a clue--if the arrow spine is off, it can cause extra noise.
How is the nock fit? A nock that's too tight will also add to the noise.
With the silencers, did you try every position, moving them an inch or so at a time? Some bows are picky, and some don't follow the rules. Had a fellow come by one day with a noisy bow, and after a lot of tinkering I'd honestly given up on it. For some reason, he moved the silencers closer to the tips--10" or so, if I remember correctly (which wasn't supposed to be as effective)--bow because as quiet as a church mouse. I've seen (heard) where moving the silencers an inch made a huge difference also.
I have to disgree that FF materials are always noisier--my experience is just the opposite, and I've talked to lots of others who have told me the same.
It is possible that particular bow just doesn't "like" that string--sometimes weird things happen that I don't claim to understand. I'd work at it a bit more first though--what you'll be giving up by going to dacron is durability, lack of stretch/creep, and reduced hand shock.
Chad