i don't think this sound is caused by a leak in the vacuum system . To my opinion its
more like a rattle of metal parts . Perhaps there is some excessive clearance in the bearing of the butterfly valves in the exhaust pipes or in the linkage system to the pneumatic actuator of the valves. Depending on temperature , angular position (open or closed) and exhaust gas speed it begins to vibrate emitting this sound profile.
I heared about a muffler replaced (V8 model) due to rattling sound at a specific load and rev range. Examination of the butterfly valve mechanism will be a good point to start with . Btw I don't think this rattling sound is normal .
Hth


Regards
Ulrich

 

I didn't hear anything other than a "hissing sound," but anything's possible.

 

You know, back in the day we used to tease people and tell them they needed a new muffler bearing... now days with all these valves, actuators, and high tech active exhausts there just might really be a muffler bearing!

 

Thanks for all the replies...think will just drive till next service and let dealer look at it.