I have a mid 2015 15" MacBook Pro. Since updating from Yosemite to Mojave recently, whenever I plug my Denon AV receiver into the MacBook to listen to music on my sound system, the MacBook screen flickers and is glitchy. This only occurs when the display settings are set to "Optimise for: Built-in Retina Display". If I set it to "Optimise for: DENON-AVAMP", the flickering stops (but it is then annoying to use, with the size of text etc. reduced). This occurs regardless of whether I am using a secondary display - usually I just want the audio through the speakers and and want to use the built-in display like normal. Prior to the upgrade to Mojave, there was no issue. Just wondering if anyone might know what's causing this behaviour since the upgrade?