Just for shits and grind, how about neutral to ground? They should be bonded together in the breaker box (and nowhere else), but if there is a fault, you might see some significant potential across them.

You’ve tried different outlets?

and it gets nowhere near those thresholds, the voltage fluctuates in the 224-234 range.

I’m assuming you measured hot to neutral, and didn’t find any transients.

Did you put your oscilloscope on hot to ground as well? A faulty ground could cause what you are seeing.

Do you have any CFL bulbs anywhere in your house? I once had a dead CFL bulb in a fixture in my basement. Anytime I turned on my basement light, every LED lamp in the house would strobe.