Hasta La Motion!

Im trying to produce a meteor effect using fluid shaded particles. However im coming up with a couple of problems which im hoping someone on here might be able to help with. This is the video

http://www.youtube.com/watch?v=rei4o4YWtgI

firstly, for the first half of the sequence the particles show a lot of jitter from frame to frame but later this problem somehow fixes itself?

secondly, about every 5th frame i seem to get a grey render which also causes a more obvious flicker type effect that looks really bad but i dont know why?

thirdly, at the moment i am using the opacity input bias linked to a userscalar to fade the particles as they age, however this doesnt look right. I want the particles to fade more realistically. What would be the best way to connect to particle sampler to control this?

any help is much appreciated,

thanks