I have also faced similar type of problem. Many have justed putting free wheeling diodes & filters at input supply voltage. You must put free wheeling diode & appro filter at inpu supply but still you will see Uc hanginh due high Voltage trasient coming on supply line due to switching ON/OFF inductive loads such as motors. Best solution for this problem (I am using it succ for last many years) is to put a zener diode of slightly higher volt at regulated supply. for if you reg volt is 5V you can put a zener diode rang from 6V-12V across 5V supply input. connect zener cathode to +5V and anode to Gnd(-ve). You just try this and all your hang probl will vanish.