vw passat sonds like muffler is broken but its not
most muffler issues happen inside your muffler and would not be visible. If you hear a rattling noise that means the plates inside have broken out(very rare) As for common muffler leaks that is usually attributed to the flex pipes up in front of your catalytic converters. after a certain age they break apart behind the mesh since its just a crappy flimsy link pipe in there. I would just have it cut out and a straight pipe welded in since its mostly just for servicing the car any ways. and if all your mounts are fine you won't have any issues. either way you can do this two ways. the first time you repair it you can just have the flex cut out and replaced the second time and it will next time blow out will be in half the time it was put in. the other option is to buy the whole catalytic converter which has the flexes attached to them. this option is the most expensive.
I agree that the flexible couplers are most likely the noise source, I'd recommend replacement with coupler pieces available through the aftermarket. I think that straight piping will crack over time due to normal flex in the drivetrain. Originally part of the catalyst assemblies.
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