You can hear it from the 6-15 second mark and through out.
2002 Mustang GT start-up weird idle sound - YouTube
Sounds like a misfire but goes away with rpms. I don't think it's an exhaust leak as I checked some youtube videos and they sound different. The sound is not continuous and I have no idea what it is. It drives me nuts.
I have an unknown to me o/r x pipe.
This started after I fixed a blown plug, and it sounds like a slight misfire but it runs good and no CEL.