Hi, I have a 2005 G35 Coupe M6.

Couple days ago I heard this weird whistling noise whenever I change gears and when i let go of the throttle.

Like when I am in second gear around 2000-2500RPM whenever I let go of the throttle the sound comes in. But when I rev the car at idle you don't hear anything.

Anyone have this problem before?

I think I know what you are talking about. Sounds like its coming from one of the front wheels. I'm still trying to track it down so if you find out before i do let me know.

i thought it was my intake

Sounds like you have a super ultra rare Infiniti TT kit
Haha, jk. Wish I could help though!

-Sean

Hey Ronnie, is that you?

Could it be a vacuum line?

Did you install your Supercharger backwards?

Nope im not Ronnie.

Ok, yesterday when I started the car, I heard this new sound which is coming from the engine when the car is at idle. This sound is different than the whistling/rattling sound and it sounds more scary, sounds like the car is going to break down.

I talked to my buddy, he said it might be the transmission =[

Does it go away after the car warms up?

This started happening after I put on my pop charger. It's probably your intake and how it sucks in air at certain RPMs. My pop charger does that at 3k RPMs

check if the air intake filter has loose screws

I've had the same thing for the longest time...No one has been able to come up with an answer or fix. Most likely, im guessing its either some kind of leak or transmission issue. Sounds like a whistling/whining noise when you accelerate after changing gears right?

It only happens when the car is cool. Its not the air filter. I dont think its the trans, nothing changes in the way the car rides or shifts, not to mention there are no leaks. But yeah 1trueg knows exactly when it happens and what it sounds like. If it were the trans i would think it would change the way the car shifts or rides, especially when i shift. I'm half way thinking it may have something to do with the belts or pulleys. Im not sure yet tho.