A processing chamber is connected to a lock chamber. For evacuating the lock chamber and/or the processing chamber a vacuum pump system is provided. The latter comprises a vacuum pump equipment having at least one vacuum pump. Further, the vacuum pump system comprises a valve device for connection to the lock chamber as well as a controller. For noise reduction, a cyclically occurring operating parameter is determined by means of the controller. From said parameter it is determined at which point in time the valve is opened such that temporally before the opening of the valve the rotational speed of at least one of the vacuum pumps can be reduced. This results in a considerable noise reduction at continuing good pump-out times.