so I have a stock a6 and noticed today upon startup a wierd sound, like a marble in a tin can, not the rattling sound but like a swirling similar to ball bearings. So I looked for it and strange as it is its coming from the intake manifold?

 

How do you know the sound comes from the IM versus the head or block?

 

I know its not coming from the actual engine itself. its either the intake manifold or the header below it

 

You still have a cat?

 

Pre detonation? As in spark knock?

How does the car drive? and hows your mpg?

 

car is fully driveable and not affected by the rattling. It only happens at around 1500-1700rpm. I went under the car and it seems to be a loose heat shield on the cat

 

it was the catalytic converter, internals were loose and moving back and forward. Threw on a magnaflow problem solved

 

Good deal. Magnaflow ftw!