Odd Flutter Noise Outside G8

[CMD]

I've recently started hearing an unusual "flutter" noise in the front of my G8. It is noticeable starting around 20mph and can best be described as sounding similar to holding a plastic grocery bag out your window while driving and the bag fluttering in the wind.

If you accelerate to 20mph and let off the gas the noise will persist until about 13 mph every time. It is most noticeable echoing off of other buildings and passing cars and can't be heard at idle or with the windows up.

Any ideas? I'm siting at the dealer now and they are unsure and even though I have an extended warranty, if and when they find the fix, if the fix isn't covered neither is the diagnosis cost. Help! I don't want to keep paying for them to try and find something that may not be covered.

[STL_G8GT]

Can someone driving beside you hear it? What exact mods were done under the hood?

[CMD]

All stock. Tech rode with me and can hear it but can't pinpoint it. Only 20,000 miles.

They are suggesting living with it since everything appears safe instead of paying for all the diagnosis costs and hoping that the end result is something covered by my extended warranty.

[-Ray-]

I would check all the heat shields.

[oesman]

Living with it would drive me insane. I second the heat shields and maybe diffuser?

[Edsel1134]

Okay let the car cool.. Take some dish soapy water and spray around the top of the exhaust manifolds.. Start car and have some one observe.. Also insure cats are tight.. Mine did this found my gasket had split

[RHARLAND3]

When my car had stock exhaust I could hear a fluttering noise somewhere towards the front while driving at slow speeds. I searched all over for something that may have been loose but nothing was. I then noticed my car had a lot of factory inspection labels attached to electrical wires, tubing, etc. There was even a big label attached to both front coil springs...I pulled those off along with every one I could find and I never heard the noise again. It's worth a try.