yo,

I just had the same proiblem this weekend!  What you MUST do is 
loosen everything from the cat back to the Y;  get yourself extra 
gasgets;  eyeball where you will need an extra one;  and then put all 
the bolts through WITHOUT tightening a thing.  When all the bolts are 
through nut'em up hand tight and then torque them.  It isn't the 
Dansk pipe per se...this is just how to do it according to a former 
head mechanic regardless of the manufacturer.  When I followed this 
protocol not a peep came from that area....the mechanic basically 
said that if you tighten any bolt {besides the head} before it is 
assembled hand tight it will never line up and consequently never tighten.

John Grazul
Rutgers University
Electron Microscope Facility