E36) Exhaust system question????

[Elysium <wonchung@xxxxxxxxxxx>]

Hello, All Bimmers.

I have some questions regarding "Exhaust System".

My baby is 328i 97, which was done emission recall in the summer.
You know there are two exhaust pipes at the back.  The right one has one
round disc panel(I don't know how to call it) inside of pipe.  I am not
sure it was made by the recall. 
Anyway, the round disc(?) is open when the engine is start.  On the other
hand, the round disc is closed when the engine is off. Hence, emission gas
is not coming out at the right pipe, which has the round disc, when I
start the engine. Only the gas is coming out from left one.

IS IT NORMAL??? If it is normal, how the right one is used.

Another question is wheel balance and tire rotation.  I am thinking of
going to local maintenance shop in order to do wheel balance. BMW dealer
requires almost 1 1/2 hours driving and high cost.

Is there any difference to do such kind of things between local shop and
dealer shop?

I need your advices.  

Thanks in advance.

Have a happy holiday!!

------------------------------