Do you mean the C4S boards specifically make a sound?

My Paramours in general make a little amp noise but I cannot say this is tied to the C4S boards.

My understanding of these boards is that they, along with other circuitry -- including the use of an inexpensive choke (inductor) permits a cost savings. Specifically, use of a modestly priced output transformer rather than the more typical expensive ones.

Is this thinking correct?

Mark