hello just re download this and notice the rain is coming inside the pits buildings, Silverstone Track 2.16
Could it be that cars were passing by on the S/F straight? You get spray on your windows from cars around, which even works when in the pitbox.
I can confirm it, but it indeed seems to be the Effect that @Lenniepen did describe above. Everytime, when another Car passes the Garage in the Pitlane or on Track, the Car gets wet and a few Seconds later, without another Car that passes it, it gets dry again. For my Taste, that Effect is exaggerated, especially when Cars passing the Garage on the Track, because that is too far away, to affect the Car in the Garage.