Can anyone help identify the problem?
 

My exhaust (most likely the case) is making some very unusual frequencies when i am accelerating above 60 mph.

The best way i can describe it is that a normal exhaust tone should be a linear tone, as in from quiet to loud when i accelerate. But now it gives a wavy frequency even when i am just gently tapping on the accelerator.

It only happens when i try to accelerate while i am cruising on the freeway, usually when i am going 60 mph or so.

Actually let me rephrase that, it is letting out a wavy frequency when the car is on low rpm and cruising?

Interesting. Can you post a video?

Stock or aftermarket?

Fast intentions with 18in resonators

I will try to get a vid when I get the chance. I was hoping someone may be able to shed some light on this

Maybe be something came got loosened and shifted causing a slight rattles somewhere. Try checking your clearance at the heat shield, cross member and even at the rear bumper.