White Streaks on a black roof

[Amaray]

I recently bought a house and it has been a dry summer. About a month ago, I noticed that there was a white streak down the back of the roof on one side. When it rains, it goes away. Now, there is a smaller matching white streak down the front of the roof in the same area as well a somewhat larger streak on the back side. I had a neighbor look at it and he thought it was dust being blown out the ridge vent and said, "if it goes away when it rains, it is nothing to worry about". Being a first time homeowner, I'm a bit nervous that it means something about the roof. It was built in 2004 and there is no evidence of leaks inside the house. Not sure if it is related, but that is the side with the radon vent which is pointed up towards the back of the house.

Advice would be appreciated.

[Patriotic]

White streak

Could be sawdust or drywall dust from construction being blown out the ridge vent. I agree with the neighbor, don't worry.