Strange noise - can anyone explain?

[barvid]

New to the forums... be gentle!

I've just upgraded my 99 for an 05 model, which is obviously a very different design inside and out. I've not driven one this recent before, but I've noticed a strange noise coming from behind my right ear (I'm in the UK so right-hand drive) when I put any pressure on the accelerator. The best way I can describe it is it sounds like a piece of paper flapping in the wind. It's not a rattle, just a sort of quiet flapping noise that only happens when the accelerator is pressed, even at low speed. Can't really tell whether it's there at high speed because the sound of the engine is too loud. I'm driving with the hood up.

It's not something I ever heard on the 99 car, but then again the interior and engine were both different.

The new car is a 2.5 Tiptronic.

Thanks for any suggestions!