My cheap DMM shows 0.6 Ohms when I touch the leads together. Was this 0.2 Ohms measurement error-corrected? If not, then those 0.2 Ohms were probably just the impedance of the leads and the points of contact.
From what I can understand, your enclosure is grounded at two places. This sounds like a ground loop, and could explain the hum you get.
My DMM shows 0.1 Ohm with just the leads contacting one another.
Do you have a source with RCAs?
Connect it and see if there is hum.
You really don't need to play anything, just connect the cables, you can turn it on, too. Don't play anything. Basically, if it's really close to silent (I have a hunch it will be) under actual playing conditions, what does it matter if there's some RFI/noise when conditions are such (ie: nothing connected) that you cannot play anything?