Moto E6 mysterious signal on test point

[Renate]

If you take off just the back cover of a Moto E6 phone most of the electronics is still covered.
But there are five little holes with a contact on the bottom.
Three of these test points measure ground, at least when I looked at them.
Two of them have this strange 4 level signal at a 2.5 V logic level.
The rate of the 12 pulses is 150 kHz.
The repetition of the chunks is 3 kHz.
What the heck is this?
(This is while the phone is operating normally.)

[ConKbot]

My first instinct was poor probe technique, but the signal isn't extending below the 0V level so, grounding may not the the cause here. The peak and fall to a lower level looks like pre-emphasis but that is a lot of premphasis for a low frequency signal, so probably not for a wired signal.  150Khz is awfully close 156Khz that some RFID operates at. Is there an antenna in the back cover of the phone with contacts to reach these pads?

[Renate]

Is there an antenna in the back cover of the phone with contacts to reach these pads?

Nope, but that's a good guess.
The back cover is plain plastic. It would have to have needles to interact with these points.
There's no charcoal gray stickers or gold contacts or anything.

I certainly looks like some kind of sync signals, there's never any data on it.
If we call the levels 3, 2, 1, 0, then 3 and 0 although they kind of look like preemphasis are distinct levels.
If it were something RF-ish, why would it idle at level 2 at the end of the burst before going to level 0?