[6 pot]

Hello, purchased an E90 330d auto yesterday evening, been great on drive home and all day today, (60 miles) however, after a 5 minute wait in the mcdonalds drive-thru, it started to rumble upon driving away, sounded a bit like a badly worn wheel bearing kind of rumble, (only in 1st gear & it seems at light throttle, once out of first gear or if you give it some throttle, the noise goes. It has continued to do this up until now. I have always been put off by autoboxes and have opted for manual vehicles as my last few automatic mercedes and volvo gave me a lot of trouble, but i decided to try again, low and behold, strange noises! It is smooth on the gearchange up or down, hot or cold, so unsure as to what it is. Can anybody give me any advice, I am a mechanic so can inspect most things as long as its not rocket science. Many thanks. Nick.