So after changing my oil yesterday and replacing with 5w-30, I've driven the pony for about 4 hours, and as the weather has gotten to the mid 30s-mid 40s range, it began making this flapping noise on cold start up. It sounds like when you stick your finger in a fan and flaps a bit. It makes it in intervals of about 2.5 seconds and the pauses are about 8-10 second and goes away just a bit before reaching operating temperature. I've never had any sort of prior noises, and it isn't heard outside of the car. It can only be heard inside the car, as if it were right behind the firewall. If it happens again I'll attach video. If anyone has experienced this before, or have any insight, it would be much appreciated. Thank you!