One of the upsides of installing the x-pipe is that each side of the exhaust system now doubles the exhaust note.

The X5's have two four-to-two independent exhaust runs. So when you install the x-pipe, you can now hear all eight cylinders in each tailpipe where before it was only four cylinders per side.

Mustangs had this problem just a few years ago and a lot of the owners installed a cross over pipe for exactly the same reason. The exhaust sounds meaner now because they can hear all eight cylinders firing out of both sides of the exhaust pipes.