Hey,
Chop off a bit of garden hose, about 1m long. Put one end in your ear, and take the other end and slowly move it around your turbo while the engine's idling. If the exhaust sound gets any louder at any point - blown gasket. Don't be too jumpy though, the change in noise is really noticeable.. and in some cases you can even feel it puttering exhaust into your skull.
Do this near the dump pipe gasket (bit that goes from the back of the turbo to exhaust) and around everything from the exhaust manifold down also.
had the same rattle - it was the dump pipe gasket for me. Your exhaust moves a little when you back off the accelerator.
Also, while you're there, crawl under the car and aim it at the catalytic converter gaskets. Mine were F***ed!
Also simple things - loose heat shield on the exhaust manifold maybe? (hopefully)
Good luck :wave: