[xDrive35i]

Originally Posted by Dukat

That's exactly the post I was thinking of. Good find, thanks!

Lotus's response explains the loud 20 seconds on the 35i start:

The "throaty", louder system is delivered on 35i models only. It uses a "Dual-Path" muffler that uses a quieter path through the muffler for light load cruising and a direct "straight-through" path during start up, at large throttle openings, and during turbo boosted operation. A electronically controlled vacuum actuator switches the muffler path.

That's the one!