'What's more likely the cause of a hdmi handshake issue?' - if only it were that simple!
'I'm getting flicker even without a source playing....' - sounds more like a physical problem rather than a handshake issue.
What gauge is the cable you are using? A heavy cable could be causing a problem staying seated in one or other of your HDMI sockets!
Simplify the system down as far as possible, disable any up-conversion in the AVR, disable Deep Color (if an option) in the AVR, try a different Input socket on the Display device, try a different HDMI cable, ensure all devices are running the latest Firmware.
Multi-cast HD over LAN solutions for Residential and Commercial installations.
The Media Factory.
Residential and Commercial system Design, Consultancy, Installation, Supply and Integration.