I have a 2008 G37s coupe 6mt . When my car is warm and I park somewhere to go to the store or something, I come back and turn it on and get this weird scratching sound , kinda loud if it’s quiet outside. Only for like .5 seconds and it goes away, it’s sometimes louder than other times. I tried looking this up but no one seems to have this problem, my friend who knows a bit about cars said it could be the starter. He said the spring could be getting stuck so it does that little clicking sound. And my other friend said it could be the flywheel but I looked up how the flywheel sounds and it’s not that. It sounds More like a little metal string scratching for a second and then goes away. I seem to notice it more when the car is already warm and has been running. Have not noticed it at cold start

 

Perhaps timing chain tensioner or timing chain guides wearing out. My Volkswagen does this occasionally for brief moment.

 

hey here's an idea, post the audio of the sound instead of trying to have people just guess randomly

 

Lol you’re right, I will laternon today .