Hi Justin and all who responded to my post. My tyres have made the same noise from new and the dealer has had the car twice for three days then again for a day recently when the BMW Technical Rep tried it. The sound is hard to define but can be described as a "hollow roaring" or "blowing over the neck of a bottle". What's more important is that it is really irritating and hugely diminishes the pleasure of driving the car. As I have said to BMW Technical; "what is the point of all this advanced technology (such as lightweight suspension and run-flat tyres) when the driving experience is ruined by the transmission of tyre noise into the cabin".
At this stage I have vowed never to buy another BMW (I go back to the 700cs in 1965 and 12 new cars since then!) or anything with run-flats, so my prime concern is what tyres to fit when the Bridgestones wear out. Continentals are the only alternative suggested by BMW for my sizes but if they turn out as noisy as the Bridgestones I am going to wish I went the whole hog and changed to non run-flats.
I think in your case Justin it may be premature tyre wear that is feathering the treads. Other forums have plenty of complaints throughout the BMW range about run-flat tyres feathering badly and getting very noisy after 5,000+ miles.
Hope your dealer can sort it for you.

Regards,

Richardl