Brownout reset general cause?

Hi,

I recently fried my atmega1284p on my sanguinololu 1.3a and just managed to burn a new bootloader and upload marlin.
Now I'm running into a brownout resets as soon as I connect to the board in pronterface. I read a discussion on marlin about this error occurring in GEN7 boards because either and LCD is connected or some resistor is valued wrongly, but find no indication that the same issues could happen on the Sanguinololu. (https://github.com/ErikZalm/Marlin/issues/174)

I measured the the 5V on the underside of the USB while connected to the main power supply and I get stable 4.68V which wouldn't be enough to trigger the brownout detection set to 4.3V.

So what could cause a brown out?
1) Is it possible that the current fluctuations are so fast that I cant detect them with my normal Voltmeter?
2) Could it be that I've blown some of the smaller capacitors and they are causing current fluctuations?
3) Could I just set the brownout detection lower? (the reprap article about the Sanguinololu list the 2.7V for the 644p) and hope the chip operates normally.

I'll appreciate every pointer