"Any thoughts?"
Yes, consult "Ott"!
His book is a real "nuts and bolts" approach to noise reduction.
Not having the book handy I will resort to my memory.
Ott emphesises (sp?);
1) Kill noise at its source (can you twist your 1/0 wire pairs?)
2) Confining the noise (better shielding)
3) Preventing the entry of noise (Shield the FP harware better, Move the FP away from the source [RF decays at 1/r^2 if memory serves me] or posibly some ferite beads on your signal leads just before they enter the FP EMI enclosure).
4) Eliminate noise after the fact (filering).
Ott probably has some other ideas in his book. I recall him going into a discusion of the benefits of using braided ground wire to handle high current spikes in ground
leads.
Another Ben