I am not too confident with command line stuff and so I am a little hesitant to get a download from the Audacity site. Unless there is a self installing version there?
I have had a further play today, if I boot the machine from OFF and don't run up anything that makes noise, Youtube, music files, any website that has streaming video or noisy adverts, then running Audacity is OK. One thing that still messes it up is to make more than one sample recording without saving the file to hard drive and then trying to analyse causes things to get unpredictable. If I close the recording display by clicking the X in the trace window it stays happy. It still doesn't like the external sound adaptor but that is not a problem as the adaptor itself is pretty rubbish. Having said that, my internal sound card has a pretty rubbish spec and huge background noise levels.
I might have to bite the bullet and buy a PicoScope which has the bonus of a comprehensive suite of software allowing all manner of manipulation of the readings captured.
Rans6........