RFI isolation

Hi all,

I have built a digital motor controller for my sync RSG.  It is 
malfunctioning due to picking up RFI on each firing of the gap.  The 
circuit is enclosed in an aluminum box.  There several wires that go 
outside the box, but they are optoisolated and I have ruled out the 
possibility of RFI getting in on these.  The RFI is definitely passing 
through the box and hitting the logic circuitry.  I have 0.01 uF caps 
next to each chip and the power supply is well-filtered.

I have tried grounding the box and leaving it unconnected to 
anything.  Could you please give me some suggestions for 
blocking this RFI.

Matt Behrend