Re: The noise of dead valve?
I have changed front and rear manifold gaskets on my V6 now, not particularly expensive (think they're about £12ea - they're individual, 3 each side). A fiddly job but not beyond anyone with a bit of patience and triple jointed wrists.
If it is this you should be able to hear a low chuffing noise on tickover if you get your head in the engine bay (more of a rasp as the revs increase)
But to be honest, the symptoms you describe don't really sound like it, i'd lean towards an engine mount maybe - if you rev it at a standstill and watch the engine for movement does it make the noise?
I know smoking is cool in Italy - but come on, don't blow the R&D budget on the ashtray