Hi Kav
So rattles make a difference ? Who knows
. Must of my flies don't have them but some do.
What i tend to do now is fish with a couple of big metal cones running free on the wire leader. This serves 2 purposes - it sinks the fly faster than my intermediate line ( and also imparts a nice 'sink and draw motion) and also the 2 cones 'clink' against each other - a bit like the noise you would get from a rattle ( only cheaper and you can alter the colour / amount/weight of the cones (the cones i use have big holes so are easy to thread and are designed for sandi tubes))
In terms of materials stay away from rabbit as it weighs a tonne when wet and so casts like a wet sock
Synthetic flash and some bucktail (reverse tied to give volume) is the way to go im my book, with maybe some wool for the head.
This is making me want to get the #10 out again...