I use an Interacter EX1205 wallmount charger with Optima batteries. The transformer used in this charger is a Total Recoil Magnetics T186. It has a noticeable hum. Adding soft-mounts (strips of weatherseal under the mounting pads) reduces panel radiation, but the transformer itself is still audible. I am trying to contact TRM to see if there is a quieter transformer to substitute, but they are hard to find on the internet. (totalrecoilmagnetics dot com) has no content, for example).
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