Is it a 60Hz kind of hum?
Go through these steps to determine the problem (listen after each adjustment):
-Change or remove batteries from the ME66 mic. I've had problems with my mics that have a AA battery in them acting strangely when it is low on power.
-Remove the microphone completely from the mix and just listen with a cable and the recorder only.
-If you have the Edirol plugged in to the wall, make sure you go off of batteries only.
Double check your phantom-power settings.
-Replace the cable with something like Star-Quad for extra shielding. Replace the cable any way - crack open the connectors to make sure there everything is soldered down right.
If all else fails, take some copper braid, affix it to an anti-static wrist-band, and see if you can drain out the ground into your body.