Michiganders I need your exhaust/noise code law help...

A guy on our local car club (MICHIGAN) forum posted about how he got pulled over for having his stereo turned up too loud. This guy has a Jeep Grand Cherokee and made the space from the front seats to the hatch a giant subwoffer box. It's crazy loud with bass, not that I am into that type of thing.
After everyone is done tossing in their two cents worth of uselessness and the thread starts dying down another guy that owns a 1972 Chevy Nova w/ 350 posts about how he has been pulled over twice in it for loud exhaust, but both times got out of it because his car was built on or before April 1st 1978. He stated the way the law reads any car built on/before April 1st 1978 can be as loud as it wants to be.

I called B.S. and so did everyone else in the car club.

Here is the link to the noise code "law":

http://www.legislature.mi.gov/mileg.aspx?page=getObject&objectName=mcl-257-707c

He is saying that because they didn't write the code until 1978 everything manufactured before that is grandfathered in. He says that if you wanted to run a muffler directly off the exhaust manifold it would be perfectly legal.

I still say B.S., but I am no lawman.

What do you guys think?

If that were true I would think there would be some pretty loud muscle cars roaming Michigan streets.