I don't really hear anything out of the ordinary. I have an '09, and when I hit bumps or rough road, I get a little noise. It drives me crazy, but it is a convertible it is normal, and expected. I know most people won't like that answer, but when you don't have a solid top, you will here some noise when there is body roll.
2009 E93 335i | Jet | Black Dakota | Grey Poplar | ZPP | ZSP | ZCW | Step | Paddles | i-Drive | CA | Sirius | HD | Logic7 | 06FL | 06NF | PDC | OEM Alarm | LUX
Retired: 2007 E92 335i
Retired: 2006 E90 330i