[slodave]

I agree that it's a ground issue. Am I reading too much into it though?

Additional info I noticed. I have yet to plug back into an amp, but I did plug into the Mbox mini and listened via headphones. I touched the Mbox itself, which happens to be metal and the hum goes away - so obviously a ground issue. My laptop - which the Mbox is plugged into, does not shock me in any way, but I know the pwr supply is a two prong, not a more conventional three prong (ground). It's possible that the wiring in my place is not grounded properly, but I remember testing that a year or so ago and things were okay.