Have a Rugged 660+ Intercom and radio and others are picking up a lot of static on the receive side when I talk. It doesn't matter if the engine is running or off, sounds about the same. I am connected directly to battery, but am not using any kind of line filter. Thinking with the engine off and no other accessories going it shouldn't be a noisy input line and must be something else? Would a line filter do anything for me here?