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[Scatty]

It sounds like the transmitted signals from wireless keyboard and mouse might be interfering with the headphones. I've had also similar problem lately, with trying out quite old wireless headphones I've bought years ago. The connection between the headphones themselves, and the receiving / transmitting station, simply terminated and resulted in constant static, nothing helped despite fully charged batteries, and switching between three available channels.
I'm also using a wireless mouse so not knowing any better I'm guessing that might be the culprit. Connecting wired headphones there is no problem at all however, so it's certainly not the headphone jack on the computer.