I have a 2017 GLC300 4Matic with the Back Up Camera. It works great but the audible signal stopped working. I am thinking that I have made a setting adjustment that turned it off but don't know how I did it and can not find a way to turn it on. The manual shows a switch located just above the light switch knob that my car does not have. So my question is how do I get the audible signal to work again, I don't really want to bring it back to the dealer for something that may be a simple fix. Thank you for any help that anybody can offer. Without the signal I find it not very safe to be in reverse.