My robust broadcom wifi card interferes with my graphic card

I have a robust AC1900 Dual band WiFi Card. Its signal is very strong and this causes interference with my AMD RX-650 card, although I had put the cards in as far slots as possible on mainboard. When using the card normally there is no problem. But when using DLNA or AirDrop services, the screen gets a flicker and eventually goes off and on again and is absolutely unusable! How can I fix the problem without making the card signal too weak and reducing the transfer speed significantly?