Is this a portable scanner you're connecting to an AC adapter? Many years ago, I made good use of a Ground Loop Isolator. At that time, I had a buzzing sound coming from a tape recorder connected to a desktop scanner. The buzz occurred during tape playback of what the scanner recorded. That scanner and the recorder were both connected electrically to the same power strip. I connected the isolator between the scanner audio output and the recorder audio input. Doing so eliminated the buzzing sound. As I understood it, the interference is related to devices that share a common ground, causing a grounding loop. If your buzzing noise is coming from the scanner speaker itself, you may try winding the scanner's power cord around a ferrite choke. A ground loop isolator is not to be used for electrical connections, only audio connections.