Weird accelerating sound coming from my '03 9-5 Aero

[MikeyC84]

When I'm driving my car, it makes this werid noise when accelerating. It sounds like a scrappy popping noise. I'm sorry it's hard to describe the sound, but from 1st to 2nd, i can't hear it. From 2nd to 3rd and so on that's when i start hearing it. If i accelerate over 4000 rpm, i can't hear it anymore. I don't hear this sound revving the engine or at idle. I never noticed it before. I only notice this sound when i have the windows down or the sunroof open. It kinda annoys me because the car should be quiet when accelerating. It's really not that loud, but it still annoys me.

Anything come to mind to what it might be?

[griffen nut]

turbo whine?

im not sure.

[MikeyC84]

I'm not sure either. Like i said, the higher the rpms go the sound will dissapear. It's only when i'm driving at normal speeds, like if i'm driving at 30 mph in 3rd gear and give it gas, the sound will appear. If i let off the gas, it will dissapear. I don't know what the hell it is.