You've probably just only noticed it. It happens all the time to me. I haven't seen a difference with regards to temperature or season.
As mentioned earlier in this thread, the eyebrows only seem to flicker when the car is turned on (that is, in "ready-to-drive" mode versus "accessory" mode). As soon as you turn the car back off (back to just "accessory" mode) and the eyebrows are on, they immediately become steady again.
I guess the difference is, the eyebrows are steady when running off "pure" 12V battery power, but flickering when running off the voltage converter from the HV battery (which charges the 12V battery when the car is on). That's all I can surmise. There must be something "unsteady" about the power supplied by the converter.
That all said, very occasionally I find the eyebrows not flickering when the car is in RTD mode. For example, sometimes when I pull up the wall in the garage at work or home, with the car still on, the glow against the wall is steady (perhaps the 12V battery isn't always being charged while the car is on?). But, more often than not, the glow is flickering until I turn off the car and return to accessory mode, as described above.
