Spikes in voltage rails
Andy is right we need more info but if I had to take a shot in the dark it's back EMF from the motors (highly inductive load) and you need flyback (or sometimes called snubber) diodes to dissipate this. Read this pdf as it explains it in greater detail:

http://www.eao.com/global/en/Downloads/technical_articles/EAO_TA_Inductive-Loads.pdf