The question stems from something that happened (pastense) back in the 1970's & 80's.
This did not happen on anything I owned. It did happen on cars from Japan as sparkchaser stated he owned Toyota's that made the noise.
I did not get a chance 30 some years ago to look into the noise as I was to busy fixing heavy equipment to play with cars and lite trucks.
Do you see where I'm cumen from now?
So, What caused the flashers of the day make the Ra Ta Ta Tat noise?