The gasket between the manifolds and y pipe can get seriously bad. In my case I was missing a bolt on each side and the others were loose. I snugged up the bolts but my awful sound remained under heavy throttle load.

Once I removed the gaskets to replace they were so old brittle and cracked that they fell into pieces. Long and short, if they are bad there is a "bridge" in the middle that seems to be able to move around once worn. Worth a check IMO.

 

And mine was so bad you could feel the puffs coming out when cold (they were quite warm).

 

I see what you mean on old brittle gaskets, but this guy just rebuilt the motor in January and said the gaskets are recrushable and to just tighten them down but that didn't stop it..
Looks like I will have to go with the SeaFoam trial

 

Cobbcj7, Did you find your leak? was just curious... and how did the seafoam induction work out for you? Im thinking of doing one myself on my DII just for maintenance ... Im kind of worried about neighbors calling police though from smoke! lol

 

You can drive down the road to clear the smoke, kill more skeetrz, and folks will just say there goes that fool in the Disco with a blown engine. Mine took maybe 10 minutes to clear out. Great fun. Did find exhaust leaks.