best luck for you, wish your dealer could figure out this problem asap. I hope this wont happened to the canadian m5 tho, it definitely a serious problem, plus you are not the only one in this formue who's suffering from this issue.
when i drove my 750, i had 2 major problems as well,
first:i need to add engine oil almost every 3-4k kilometers which is not normal at all, the car drinks the engine oil rapidly fast;
second when the engine is is revving about 1-2k/min, especially in first and second gear, there is always a strange sound, they never fixed that problem for me. They tired to fix it, after 3 days the problem came back, always happened in winter, eventually i gave up because that was a leased car.
sorry for off topic, again, wish they could fix your car properly