rough idle

Just very recently bought my first M5, an 06. Serious question: When I first start it in the morning or after sitting about 11 hours at work, it idles very rough for about 15-20 seconds, like an older carburated engine when the choke isn't quite right. After about 20 seconds or so, smooth as silk. Is this "normal"??? Some have said it is a characteristic of the V10. Thanks