Everytime I run my car on the road a high pitch or whine noise is coming from the engine bay. I don't really hear it at idle but hear it loud and clear when I hit around 40 mph, everytime I step on it a little it gets louder and when I let go of the gas it stops.... Any idea what it might be? i thought it was my back tire since it has no tread left but i doubt it

 

Lemme guess.... You recently bought a used G35 and this high pitch noise happens when you drive it it? Most likely you have an aftermarket intake. I have an Injen Short/CAI which also makes this sound. If you do have an aftermarket intake, it is absolutely normal. It actually sounds pretty cool. Kinda like a Turbo hahaha.

I know this because my friend also has the same intake as me and our cars do the same high pitch sound.