Babbsack:
Dear krupski,thank you very much for your last posting giving me some ideas what to do...
To realize all your ideas I have to find some people which have the required equipment and in my eyes the required know-how. Sorry if it will take some time go give any response.
For all your effort: +1 karma! Thanks a lot!
building on @krupski advice, you could try simply adding a capacitor across VIN and ground on your Nano. Something substantial, like a 47uF electrolytic. That may help with a power ripple. If it doesn't solve the problem, then that narrows the problem down to perhaps the power regulator on the board.
It's a 50 cent part.