Clouds flickering - need help on CG Short
 

We've been using a geometry solution to making our Heavenly clouds for our short film but we're having some flickering problems and Id love to solve the issue or find a good replacement.
http://dl.dropbox.com/u/1289261/Devi...avenly_Sky.jpg
YouTube - sh0010_sky - CG Animation - WIP Render - Devils Angels & Dating

We had an earlier version that looked flicker free but don't seem to be able to reproduce it now after a few years of evolution and changes. If anyone knows a good way to fast rendering clouds or would like to join the project to help out please let me know.
YouTube - Cloud Test v01 - Devils Angels & Dating - CG Short

Here's our work in progress teaser trailer so that you can see what we have in mind:
YouTube - Teaser Trailer v72 - Devils Angels & Dating - CG Animation Short Film

Our main development site is here:
http://devilsangelsanddating.com

are you using fluids for the clouds?