What you are really asking for is a cure. Sadly it's never a sure fix unless we reduce what parts are receiving that interference signal reception capability. I see you already tried chokes but you may have to go back to what worked before. Drop the third monitor as a test.
Remember you are talking RF physics here. That radio emits a signal and something is receiving it and getting upset about it.
To resolve is going to be specific to that setup. If you are unlucky that the issue is compounded by a reflection of the RF source that doubles the power then simple solutions will not solve this. You may have to swap in another PC that is more immune to the source.
I work at a retreat center and we use Motorola walkie-talkies to communicate across the property. We recently moved to a new office and now my coworker's monitors blink off for several seconds whenever a walkie-talkie is used within 8-10 feet. This has never happened before, even when using the radio while sitting at his desk. My PC is within 2-3 ft of his and never has any issues.
Upon doing a little research, I found out that it's possible for radio waves to interfere with PCs, but very little has changed about his set-up, so I have no idea why it's a problem now but never before.
He has a Dell Optiplex 3020 with an Intel i5 processor and is running Windows 7 Professional. The only changes are that we added a third monitor (all Dell monitors) via a USB to HDMI adapter and put the monitors on a triple monitor stand.
At first, I thought that the metal monitor stand was acting as some sort of antenna, but if that is removed, the issue persists. I've added a number of ferrite chokes to the HDMI and VGA cables, but they don't make any difference. Anyone have any ideas what the issue is?

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