From what I've read elsewhere, it's most likely a switching power supply - and it's probably right here in the shack. They radiate a "warbling" sound. And they drift. And I have a bunch of them in-house.

One day when it really irritates me, and I don't have the computer turned on, I'll try turning off the UPS to see if it's the laptop power supply. It is located quite near the antenna cables and radios and is the most likely culprit.

If it turns out to be responsible, I'll try moving it farther away and wrapping the power cord(s) around some ferrite.

Thanks for all the suggestions! jta

America needs a sense of humor...