Your symptoms point in that direction. I don't know if termination is required in general for those things, for sure it depends on your ground plane and trace lengths. I'd give it a try with an AC coupled end termination for the clock signal, or a source point series termination. One of these usually cures the ringing. 9MHz isn't that fast, yes that's true, but these modern CMOS chips put out quite fast edges, and the inputs might be sensitive to ground bouncing or noise at way much higher frequencies, causing the flickering.
Configuring the micro's output pins to a less powerful drive / slower edge might also help (many modern uC's have these settings, and often default to fastest, sometimes slower is better).