So, more than likely I am being an idiot here but my 04 G35 coupe has been making a whistling sound when I really punch it. The closest thing I can compare it to would be like a turbo whistle when I am accelerating, and then it stops or winds down a bit when I let off the gas. A) is that normal? B) what causes it?

 

^
Some possibilities

1-Vacuum leak?
2- head gasket?

Do a compression test

Telcoman

 

the intake couplers are made of sub par rubber, check those especially the accordion one

 

Mine does something similar, but it comes from the speakers and sounds just like a supercharger. When I flick my headlights on and off it goes away. Non-car friends tell me it sounds cool xD

 

when i had my 5.0 mustang, the cone air filter was slightly bent and caused a little whistle sound when giving it certain amount of throttle.. at least i think it was the air filter.. it's most likely something from the filter to the throttle body causing that.. like he said ^^^ check your couplers and connections..

 

Likely an air leak. After I put on the plenum Spacer I got a whistle only from 2700-3000 RPM which sounded cool. If it's always making whistling you have an air leakn