430 Rubbing sound at high speed

I've noticed lately on my 430 scuderia that at high speed I'll start to hear a rubbing/fluttering sound almost like if you stick a playing card in a fan. Sounds like it's coming from behind my left ear. I checked both driver's side wheel wells and couldn't find anything that looked like it was rubbing.

Here's a video clip, you can hear the sound start once I'm at the top of 3rd into 4th gear.
Any ideas? Thanks!

 

No, it happens under accel and decel and any gear.
What triggers it is going over a certain speed, which makes me think it's something bending under the air pressure and rubbing.

 

I looked under the car and didn't see anything hanging/sticking out visually but that's a good suggestion, I should get a closer look.

 

Just put on the Kline inconel exhaust a few weeks ago, I absolutely love it. Sounds exactly how a Ferrari should sound imo, that high pitch "F1" sound

 

I just wanted to report back that I solved this.
It was the exterior window seal where the top of the door meets the bottom of the window.

That seal on my car shrunk a little and there was a gap where it meets the side mirror. I simply pulled/stretched it back to close that gap and the sound is gone.
Apparently wind was getting into the door at high speed and making a fluttering sound.