Heat Riser/Plug !?

["Mittal, Vikram (SUPP)" <Vikram.Mittal@supply.ge.com>]

When I started my 1990 100 yesterday,  I felt that there was more noise
than usual
coming from the catalytic convertor area.  

Suspecting a leak I took it to my local muffler guy who put it on the
lift.  What we
found is that there is a small tube on the cat. itself pointing to the
back of the car.  
Some amount of exhaust gases are being expelled through this.

Now I am not sure if this is correct or not.  The muffler guy assures me
that this 
is something to do with the engine and can only be fixed by an Audi
dealer.
Additionally,  he refer's to it as a "heat riser/plug" !?

I am surprised that I have never heard of such a thing and also that my
muffler
guy was actually turning away business saying that only a dealer can do
this.

Can anybody shed some light on this ?  I am going to continue using my
car
as if nothing is wrong.  Is this a good idea ? The car has 104K miles on
it and the
original exhaust system and oxy sensor.

TIA.


Regards,
Vikram.