I suspect the earth wire is likely to be a primary radiator!
I think it needs to be pointed out that any metal box needs to have no
slots or holes larger than a small fraction of the wavelength. You need
some sort of RF gasket or fingers on the lid to ensure that there are
multiple points of contact around the LID. PCs are probably impossible
to screen at microwaves, except by screening the whole room; they have
big holes in drive bays etc.
This is basic theory - I've had little success in screening PCs, even on
2m. Most of the amateur radio EMC books are too simplistic in my view and
the professional ones are very expensive (and a lot of knowledge is probably
within the industry not in books).
For future reference, does anyone know sources of finger stock available to
those not in the trade?