Weird noise from gas cap
 

Here is a video, what could this be?
https://www.youtube.com/watch?v=va2cVbNayT4

There is a valve attached to the filler tube that fails. Pelican has lots of photos on how to replace it. You need to remove the wheel well liner.Have you had trouble filling with gas or CEL?
A good while-you-are-in-there job is to relocate the emergency cable for the frunk.
Good luck !

After I fuel up the car, I have to crank it for quite a while before it starts. This started a few weeks ago and the check engine light came on.

How did I guess?
Pelican has the diy for you.This is for 996:
Replacing Your 996 Fuel Line Vent Valve / Bleeder Valve - Porsche 911 Carrera & 986 Boxster - Porsche 996 Carrera (1998-2005) - Pelican Parts Technical Article
https://www.youtube.com/watch?v=zulI06TPBVc

I had the same issue. So I made a rod which I manually push and pull with the door open (RHD). At least it makes my mind at rest.