[D]

On Oct 24, 1:04 am, "Richard Crowley" wrote:
"D" wrote ...

Microphones with a battery do not hum. Why?

Because the battery is independent of the mains power.

That confirms that the problem is coming from the mains-
derived microphone power coming through the sound card.

How to make microphones without a battery not hum?

Replace the sound card with one that works properly.
(Or just continue to use the battery.)
Thanks Richard Crowley for your answers!
I have two cards: SB Live ct4830 and SB 16 PnP. They both hum from a
headset microphone.
Best regards,
Dima