As any radio amateur will tell you, PC shielding in the wild is generally poor. Plus the vast majority of PC RFI is radiated via the connected cables ( be that USB or the power cable ) or the monitor which form broad-spectrum antennas.

A PC and its appendages is a horrendous radio squawk-box and should be kept away from anything RFI-sensitive. The FCC 'must not cause harmful interference' clause is pretty worthless.