Last weekend I noticed my 04 3i seemed to be downshifting in the 4th gear even though I was NOT accelerating. And once it would downshift, it would almost clunk or bang down to the 3rd gear. It has never done this. I took it to the dealership and they ran a diagnostic and found nothing wrong.. the check engine light never went on either. They said they even test drove it for 30 miles.. has anyone else experienced this before? please help!