[D]

On Oct 17, 1:44 am, "Richard Crowley" wrote:
"D" wrote ...

It does not hum when no headset is plugged in.

Then you can eliminate any problem with the computer,
the sound card, or any software including drivers, etc.

One of the headsets is brand new and checked.

What does "checked" mean? Do either of the headsets work
OK on another computer?

Yes, the hum changes when I move the headset around the room: the
further from the computer case the louder.

I would take a wild guess that it has a shielding or grounding problem.

Yes, it hums when I try using a differen computer mic: both headsets.

The problem may be with the basic design if both headsets
show the same symptoms.
Thanks Richard Crowley for your suggestions!
The hum is from speakers, not from the case.
Yes, either of the headsets work OK on another computer.