That is a frustrating problem. Does it prevent you from using digital modes, like packet and Vara?
If so, have you considered using ferrite beads on the signal wires and even the power supply leads? Is the antenna far removed from the transceiver? Have you considered using ferrite beads on the feedline to the antenna?
There is a troubleshooting guide: Troubleshooting Digital Modes – digirig
Also congratulations on your DIY digirig, which you presented earlier. I noticed that you use an insulating material for the case:
My Digirig has a metal enclosure. Have you considered a metal case for your Digirig to suppress RFI?
73 Constrainted