The Audi TT 3.2 and Volkswagen R32 both have a exhaust system made for VAG by Remus Racing. The system incorporates a "flap" that restricts exhaust flow in order to keep things quiet. The flap opens after about 2500RPM (from my experience, R32 owners seem to have this much higher, at over 3000RPM). Most of the "research" I've read comes from R32 owners. Of course, the packaging in a Golf body is very different than a TT, and the flap appears to be one of those differences -- it's on the left side of the R32, and the right side of the TT. The flap is intended to provide a quieter exhaust when full power is not requested, but improved breathing and increased power on demand. The flap is controlled by a vacuum switch -- a vacuum hose introduces negative pressure on a small piston that pulls a rod, and turns a crank that closes the flap. Basically the manufacturer is trading quiet for efficiency, as the flap increases back-pressure on the system. In this "mod", the flap is forced to stay open by one of two methods: disconnecting and capping the vacuum hose, or pinching the hose closed so that no vacuum is introduced to the chamber. Here are a few examples of the clamps used by R32 owners from the VW-Vortex:
If I'm looking at these pictures right, we can clearly see key differences between the R32 and TT 3.2 -- mechanically similar cars but the R32 is rated at 240hp, and the TT 3.2 at 250hp. Refer to the picture below left that shows the connections around the R32's muffler and the diagram below right that shows the components of the TT 3.2's exhaust system (from the Bentley CD): the R32's B-pipe elbows to one end of the muffler, the TT's enters strait; the R32's flap is on the muffler inlet, the TT's is on the left exhaust port; the R32's exhaust ports, set wider apart, elbow 90-degrees from the muffler; the TT's exhaust ports, set much closer, come strait off the muffler body; the R32 has a canister style muffler body -- a tube with two end-caps; and the TT has a muffler body made from two formed "tubs" with a single seam. The B-pipe in both cars is set to the left of center, so even with the flap closed, the TT should get much better breathing than the R32 -- the open port is on the same side as the B-pipe, and there is no extra plumbing. Admittedly, I'm just guessing at the effect of all this, but -- hey makes sense, right?
On the R32, the vacuum flap is in the U-shaped piping upstream of the muffler, and the switch is set very near the heat shield separating the exhaust from the left-rear wheel well. On the TT 3.2, the flap is downstream of the muffler in the exhaust port itself. It's the mass of pixels to the left the number "24" in the diagram above. Below is a look down the throat of the right-hand exhaust port of the 3.2TT (sorry, it's not washed -- hey, it's cold out!). You can see the flap is currently open, and the switch is to the left of the exhaust, as pictured. A closer look at the rod, and you can see that it's just a simple bent wire -- on the R32 above, it's a much more substantial rod and knuckle design.
So, I prepared a kind of small plastic clamp, and also had a small steel C-clamp. I was also prepared to remove the hose and cap it with a screw. But when I looked under my car and saw this slightly different arrangement, I realized: the vacuum switch is set on the side and is much closer to the road, the vacuum hose is packaged tighter and is harder to remove, and a clamp might get hot and melt (plastic) or damage the hose (metal). The other consideration is that this mod must be easily reversed. So I took a closer look at the pieces, and tried a few things.
What I found is that it is very easy to slip the bent wire out of the small hole in the crank plate. However, since this in no way de-activates the switch, the wire would still catch the crank. So I, very carefully, tried turning the wire 90-degrees -- and it turned quite easily. And that's it -- the flap stays open, but the switch stays active. Easy to mod, easy to un-mod when I go to the dealer for service or for an inspection. I am not bending the wire, just slipping it "out of socket" and then turning it with the piston.
The above left image shows the wire rod, turned 90-degree so the tip is sticking right into my index finger. The above right image shows the wire rod now pointing strait back to the muffler body. A quick test drive confirms the slightly louder and lower exhaust note. Excellent! It is not a "rip your ears", fast-n-furious kind of sound, but the sound of a well tuned sport exhaust. Only a couple things bother me about this: the flap is free in the exhaust, it's not being positively held completely open; and the vacuum switch, no longer restricted, is moving further and with more force. I'm concerned the switch may wear prematurely -- but not very concerned, cause I'm not really sure I want it there in the first place. I think the force of the exhaust pressure should keep the flap open, though if it were held open, I could be sure I was getting the most efficiency. R32 and TT 3.2 owners -- please feel free to send me your comments and ideas.

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