Hello, with my Mazda 5 CW more than 5 years ago a trailer coupling was installed by the previous owner, I bought the car like this. For a few weeks the following problem occurs: When braking it hums out of the control unit back, which is annoying permanently. Whether this works with trailer operation and all the lighting, I can’t say, since I don’t use a trailer and if, then once in ten years. It was easy. In the engine compartment next to the battery are various cables, there are also any terminal, everything is lying there loosely around, does this have to be connected to the battery plus and minus? Mazda has performed the installation dealer, all the documents I have there. Can someone help there? Maybe someone from Heilbronn comes and knows with it well and can check it? Thanks and many greetings.