Something is a bit fishy to me ...
There should be negligible ripple on the Input side with NO load. Can you check that?
You went from 1,000 to 15,000uF and saw NO reduction
What was the current at that time? Can you estimate it, if you don't know exactly?
Do you have 0.1uF ceramic caps on the Input and Output of the Reulator AND/OR ~4.7-10uF Tantalums or similar ESR?
Is the MPU circuit any distance from the Regulator? Do you have a 0.1uF cap on the MPU PS pins? Any other 0.1uF caps?
It does seem excessive to me at least.