I posted this on the WO5 thread but I will repeat it here.
The answer is so simple. We did it as school boys. Just a piece of bicycle tube and the stick from a frozen sucker. F1 exhaust is a bit bigger so use a motorcycle or car inner tube.
Nice video of the effect:
The video really puts the whole idea of manipulated exhaust noise into proper perspective. Come on Bernie & FIA - is that really any different from what you are asking for. Its all fake.