I have the same problem, I think it's where the car has recently had a full valet and not had time to properly dry so there is still moisture in the car. It also does not help that the car is warm during the day, and when the temperature drops rapidly, there is a problem.
Remove it and spray it out with throttle body cleaner, then Use a soft toothbrush on any stubborn spots. This worked for me, but I just did it as PM, not due to a problem.