It sounds like you might have a loose or split boost pipe, they come from the turbo at the rear of the engine, to the intercooler then up to the inlet manifold, I suspect one of the connections is faulty most likely.
Exhaust leak? There is a bunch of stuff that could cause this problem. The Passat TDI has an assembly problem with one of the intercooler hoses, the one that comes off the metal cross pipe. They built them so that a ground wire rubs on it and makes a hole. The solution is to loosen the wire and bend it out of the way, and tighten its nut again.
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