rev up and down on 1999 BMW 328i

hi, i have a 328i steptronic. when the car is moving the rev will down up and then down and then up again esp on an incline. On an incline the rev drops so must that i have to change the gear manually. at the same time, there is a noise at the left back. i tried everything, please help.

Asked by for the 1999 BMW 328i
Did you find the solution to this problem? Did you have to take it to a dealership or somewhere else?