Hi thank you for going to the trouble to do all that.
I've got all those settings. Like I said I tried it on other machines, and also different parts of house.
The software I am using is the Win 10 camera app.
So I tried voice recorder and it's the same problem.
I have the lifecam app but it doesn't detect the lifecam (!).
I also use a logitech webcam, and that doesn't have any audio interference or hum.
Which means it's got a better microphone or is better shielded.
There's always a whiny hum with the lifecam. When I adjust the microphone input level to 30% it's not badly intrusive, but everything is quiet.
Any more than 30% and it gets bad.
I should add that the microsoft online store has this lifecam for £39.99, and that's way overpriced for something with bad audio.
And, no, I'm not working for Logitech :-)