Doepfer

hi
i just installed an a-199 spring reverb module in my a-100 (suitcase 
model) and i can't seem to get rid of a bad hum from the unit. i 
mounted both the actual reverb mechanism and the control panel in the 
upper left corner of the case, as far away from the power inlet as 
possible--but still: hummmmmmmmmmmmmmmmm.
does anyone have some tips how to silence this module?
thanks.
jason kahn