Bathroom exhaust fan dripping water

Wasn't sure where to post this. If I'm wrong, tell me where to go! When the temperature in my attic gets low (probably below freezing outside), I get water dripping from by bathroom exhaust fan. I am pretty sure that this is coming from the condensation caused by the difference between my interior temperature and my attic temperature.

I have pulled the exhaust fan and made sure It's clean, I have vacuumed out as much of the vent tube as I can get to, and I have ensured that there are no dips in the vent tube routing.

Does anyone know what the cause of the drippage is and how to stop it?
Thanks,
Chris

 

You didnt say if the flipper damper there is closeing all the way. The one on the fan and the one in the roof vent. this would stop the warm air from the bath going up in the vent pipe there. When the fan not on.

ED

 

There's a damper in the fan housing that I lubed. There is no other damper.

 

You should have a damper on the roof vent there also.???????

ED

 

I also had water condensing in the exhaust vent. Eliminated the problem by using insulation over the vent. Used 5" Flex HVAC insulated ducting available at home improvement stores.