trying to find source of vibration

I HAD A BALANCE WEIGHT FALL OUT OF A FRONT ROTOR ONCE. tOOK A LONG TIME TO FIND THE VIBRATION! I GOT LUCKY AND A OLDER FRIEND OF MINE HAD ONE OF THE OLDER ON THE CAR WHEEL BALANCERS WITH THE STROBE LIGHT. that's HOW WE FOUND IT. JUST A THOUGHT.....