Dell Optiplex 7040 small form factor monitor goes to black

We have had a handful of Dell 7040SFF monitor issues. The user will be in the middle of something-online, email, reading documents and their monitor or monitors will go completely black for about 30 seconds. 

Windows 7, 64-bit, 8 GB ram, Intel i5-6500 CPU

I have updated the bios, chipset, and installed the video display drivers and control panel. We have Dell monitor P2014H Flat Panel. 

I even went so far to have a user's motherboard replaced. STILL that did not fix the issue. 

This investigator with the issue(we are the sheriff's office) figured out the problem...

His 800 MHz police portable radio was the problem. If that radio is less than 4 ft away from the 7040 the monitors do not blank-out. So fortunately that is an easy fix.