MFD lines/pulsating

I changed the serp belt and afterwards I noticed what looked like scan lines (moving lines of different brightness on the background) on the MFD. And I was thinking gee maybe the belt is too tight, but obviously it is unrelated as there is no alternator.

Anyways, I have an old 12V battery and what happened is I was running the radio for a long time in ACC and I believe the lines were cause from the DC-DC sending large charging current to the 12V battery and also adding voltage spikes to the 13.9V. (It has do to with the inductors used in buck voltage regulators and a large current and/or back emf stuff with the generator motor). Eventually the lines got smaller and went away and they were not present when the ICE was not running. So probably related to MG1 and/or the DC-DC system.

I just thought I'd mention it for kicks. If you see lines on MFD when you start the car, you probably need a new 12V. I didn't have a scope, but it might make for interesting plot. I'm guessing the spikes were at the frequency corresponding to the rpm MG1 spins at idle.