I have a 2011 is250 and this flapping noise just started out of nowhere! I can’t tell if it’s the passenger side front or real...but the faster I go, the louder it gets. When I release the pedal, it stops. Driving me insane! Anybody have any idea what it could be?

 

So if you're driving at HWY speed and you let off of the throttle the noise just goes away?

 

Yes. The more gas I give it, the louder it gets. Sounds like it’s coming from the passenger front of the car.

 

Have you looked underneath to see if the underpinnings of the car are all fastened and tight? Look under the hood , under the car , etc. Perhaps you’ve even run over something and it’s stuck underneath.

 

Could be rusted out exhaust heat shield.