I've got a 2013 C2 coupe 7MT with 25k miles and no mods. This is my daily driver and I don't usually jump on it. However, I just noticed a "cricket chirping" sound coming from behind me when I get revved to over 5000 rpm to the redline. I assume it is coming from the engine but can't swear that it isn't some weird harmonic rattling from loose trim. Anyone else experience this?

 

Never heard of this- I had a base 2008 997 that never did that, but that was the 3.6 liter engine.
How dirty is your air filter?
Have you had a tech take a look at the air intake?

 

Have a tech look at your serpentine belt (it's in the back&#128522. They make that Chirping noise when loose or slipping on a pulley.