My G37with manual trans does the same thing. I only just noticed it because I listen to the radio and stereo much less since doing some mods. I installed the Stillen Catback Exhaust and the Stillen Gen 2 Intake system, so now I like listening to the engine and exhaust sounds more than music.

It sounds harmless enough and maybe it's the result of the mods. When I play music at just about any volume the sound can't be heard.

The car is running perfectly so I'm not gonna worry about it.

 

I did some hard driving today on one of my favorite twisties, and this particular sound has disappeared.

 

has nothing to do with mods mine does it stock and with an intake dealer says its THE VVEL