We have a 2014 GL450. When we first purchased we could not hear the rear parktronics sensor at all from the front. My grandson could hear it from the rear seat but my husband and I could not. We took it to the Mercedes dealer and they said it was at 80% and turned it up to %100 but we still can barely hear it. Mercedes said that is just the way it is. They said it is a convenience feature and not a safety feature and they can't do any more about it and to use the camera. I just want to see if anyone else had any issues and what they did. If yours works fine how loud is it? I know our ones in front we can hear just fine. To me this really seems like a safety issue.