Yes, at least the muffler is different. I have an '05 with SP and it did not have a different muffler but BMW does make a "Sports" muffler as an aftermarket type option for it. I saw some for sale on Ebay too. That's probably the one that comes standard with the '06 SP.

Thanks for the info, I think I'm going to try the golf tee mod!

I did the "golf tee" mod right after I picked my X3 up from the dealer. At first it sounded nice, but then I noticed that the sound would resonate through the cabin more around 2K RPM. For me it was not a good quality rumble like I had with my Borla on my last car. If you want good sound you will have to go with an after market system.

I just tried it. Only notice it around 2K RPM also. Not sure if I like it or not. I'll try it for a couple of days and see. I didn't detect any loss in power.