On some cars (like mine) you need to make sure all your indicator bulbs are the same wattage. For some reason if I have a different one then the boka will make one side indicate faster than the other side. Sometimes a blown globe will also make the boka go crazy.
It could be your battery but I doubt it 'cos if the battery is suspect then you'd have a hard time starting the car, running the engine, headlights, etc. These items suck heaps more power than your boka.
seeyuzz
river
PS: When I say "boka" I'm referring to that thing in your car that goes "boka boka boka" and makes the indicators flash on and off. I'm sure it has a proper name, but to me it's the boka.