the name originated from the characteristic muffled noise it produced when operating; alternative names puckishly given the device by Polish Cipher Bureau personnel were "washing machine" and "mangle."

http://en.wikipedia.org/wiki/Bombe
but they were more prosaically described by operators as being "like great big metal bookcases".‏²

Perhaps the truth lies closest to a Cipher Bureau technician, Czesław Betlewski: workers at B.S.-4, the Cipher Bureau's German section, dubbed the machine a "bomb" (also, alternatively, a "washing machine" or "mangle")

The first Bombe machibe (named after the ice cream, not explosive)

code name Bobma (the Polish word for ice cream)