Alternator noise, new

[Dorfie]

Hope you can help me where to start looking. This is happening to the plane I am flying while building the RV. It is a 24V system. Plane is Socata TB10 with 0-360 engine.
The alternator makes a "crackling" type sound, mostly RPM dependent. It comes through either of the two comm radios. It goes away when the switched radio is turned off. It used to make the noise only above 2500 RPM, but today it is audible as low as 2300 RPM and getting worse I think. Best I can describe it is that it sounds like a bad connection or "arcing", but none evident. It is not a "whinning" noise. The alternator has a suppressor on it. When I turn the alt field off, all goes quiet. The charging (voltage) remains steady at all currents drawn. The more current drawn the quieter it gets and basically stops when I have all switches on. Alternator is externally regulated.
Thanks.
Johan