Here's another insight...

I have heard the same thing twice in my car. Both times I caught a glimpse of where the noise was coming from. Both times I heard it the tiny little red light in the "snowflake" AC Button was flickering along in sequence with the sound. Next time you hear it, pay attention to that light. I have a Verizon phone, so I don't know if it could cause this or not. Before reading this. I attributed the problem to be related to my AC Fan speed switch problem.