Dinan's exhaust on the E46 M3 and E9X M3 both have fake tips. One pair of tips on te E46 is fake. You can only really tell if you look at the water vapor coming only from one side during a cold start. On the E9X, one tip on each pair is inactive. On both stock setups all tips were active but required lots of extra piping which increased weight and hurt efficiency. Dinan's setup is more free flowing but required it to be this way to get the results they wanted. Also on the E9X there was horrible drone when a y-pipe was used to make both tips on each pair active.
Click on "Dinan's E90-92 M3 Exhaust"