There are so many noises that people complain about that are completely normal for this engine that I'm half tempted to just tell you it's normal and be done with it.
Inspect your belts if you suspect them. An audio clip is very helpful if you're looking for interweb diagnostics.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |