yeah, just ground it to your case... I dunno what supply wires are like in the US... do you guys have 3 prong cables? or outlets? in Aus we have 3 outlets - 1 to live, 1 neutral, and a direct earth. By law all electrical equipment that isn't double insulated (means all electrical components are totally isolated) MUST have an earth connection (in Oz at least).
What I am working around to is "is your pump grounded?"
Also, I just did a bit of research, which popped up this for me
Some college's stuff on EM shielding, which I definitely trust more than anything else I could say...

seems I might have been on the wrong track before...
Hope you manage to lick the problem...
Cheers, Komic.
edit: changed uni to college in URL. /edit
[ 10-29-2001: Message edited by: Komic ]