From time to time, I also experience this - it's intermittent at best. While annoying, I just let it pass. Never brought it up with the dealer.
Current: 2012 535|| Titanium Silver, Black interior, M-sport, Premium, SAT, Nav, Apps
Retired: 2010 535|| White, Natural Brown interior, Sports, SAT, iPOD, Rear airbags
Retired - 2008 528 - Premium, iPod, Cold Weather, Titanium with black interior