Feels cool in duct

I recently replaced the duct and outside vent cover to my bathroom because a bird was living in it. While going to install the fan today I realized it felt pretty cool inside. Almost like there was a small draft. There are no holes or anything in the duct, and I put silicone around the vent cover as the instructions stated.

Now I'm pretty new at doing these kinds of things and was wondering if this is normal. Thank you!