[playbass06]

Try instead, putting FG back to "Draft," (it's more of a personal preference, but it tends to give you good results in little time, good for base settings) but then go to the Render Setup window. On the Indirect Illumination tab, in the Final Gather section, there should be a parameter named, "Rays per FG point." Try increasing that (default 50, try 150-200). I'd probably not go over 300 rays with that, it gets slow.

I'm not sure how much this will improve it, but it could help. It looks more like a shadow issue in some spots, and less FG. Have you tried increasing the Soft Shadows Precision multiplier?