I am glad you got the results you hoped for.

With all those ground loops and the probe cable also, I'd expect much more noise of that!

Usually to measure noise on a regulators rail, you would ditch the cable with the crocodile clip and use a coil spring to earth the probe as close as possible near the tip.

Adding so much capacitance, from a certain point on, is not worth it as much as have good grounds.

Congrats,
Ioannis