This may seem like a wierd question, but I'll bite the bullet...
I was at the airport the other day, and while a 737 was taxiing, its beacon light was flashing, as usual. However, they werent in sync, and it seemed like they (the one on the top and the bottom of the fuselage) tended to speed up and slow down. It was like they flashed at the same time, then one on the top, one on the bottom, then it got slower, slower..finally maybe a two second pause, and they continued to flash.
Why don't they just flash together?