I recall some years later a young graduate engineer coming into my office with a rather involved circuit consisting of 30/40 TTL ICs and complaining that he'd double checked the circuit and it still didn't work. I took one look at his device then went to the draws of capacitors and handed him a handful of 0.1uF ceramic caps and told him to put them between the ICs' PS rail pins to ground which he did and to his amazement the circuit worked immediately.

He stood in amazement that I should have such insight so as to fix the problem at first glance.

How such critical knowledge can get lost in university training these days just amazes me.

Unless you have a 50MHz buck converter (which would be very exotic --- the fastest common ones are around 1/10th that), that looks more like something may be inadvertently oscillating and/or you're picking up strong RF noise from possibly something in...

https://en.wikipedia.org/wiki/6-meter_band#Radio_control_hob...

And "leared" -- the (unintentional?) pun made me click.

You could also try just sticking a 100n and 10n across the smps output too.

Another lesson waiting in the wings from mounting a magnetometer in plane and right next to four BLCD motors, lmao.