Most of my Edit pinions have 'sand damage' and sound fine. As long as you get the grit out straight after the run it should be fine.
It could be something as simple as the make of pinions you have that causes the screaming noise. I once had some RW pinions and they made a horrid noise. Once I got some new one (different make) the noise dissapeared.
OR, the mesh is too tight. try loosening the mesh on the spur/pinion.
Other than that Id do as suggested re-shim the diffs. and also make sure you don't over tighten the gearbox tops. This can cause them to clamp the bearings and cause them to bind.
The rattling noise probably is just loose shafts clattering on the outdrives. may be woth getting some of the Edit litghweight versions and use the drive blades on the shafts. it nothing to worry about really. I've been running my Cyber with loose shafts for the whole of this season and it hasn't caused any problems.
