As said above, you can easily get the "dump" noise from the DV by fitting an open cone filter, or CAI (better as it relocated the filter out of the engine bay). The noise is then audiable outside the car, and sounds smart IMO. As for "chatter" this is generally not something that you want on a VAG 1.8T as it is bad for the turbo as the chatter is caused by air flowing backwards through the turbo vanes, putting excess stress etc on the turbo. As for external wastegates i wouldn't know, never heard of anyone fitting this, maybe somebody else can shed some light?