Not exactly true SirSparks, that's why I was trying to say the exact form of the spike is all important, because if it's a simple high voltage rebound from cell resistance it's a tiny tiny little spike, just enough for the regulator to fault out at by registering, if it's basically a regulator response issue with the change in loads it might be more problematic to fix with a capacitor, again though it depends on exactly what the nature of the spike is.
Crut, interseting term usage there, never heard of a hash filter before. I'd call them chokes.