When I used to work on analogue audio, we used to laugh at PC based measurement systems - because the one thing you don't want anywhere near your test circuit is a PC (especially in those days). Now I guess they're a bit better.

Also used to to walk around turning off lights, soldering irons, anything else, to try to get the meaured noise down by a few dB. Especially if you could see that telltale 100Hz component in the detector output.

Must have been a bit nasty to kill your display though.