This is an issue with power being delivered across two flat molded cable connectors and the small gauge wire in the cable itself. Every time power fluctuates, it is exaggerated at the load (monitor). If I could find which pins on the connector are power and ground. I would add a couple of hundred micro-farad electrolytic capacitor to act as bulk decoupling for power at the load. At some point when I have the time, I’m going to track down a power and ground point on the monitor, I’ll verify the results. A couple of high frequency decoupling caps might be in order as well.
The consequence of using a flat molded cable.