The circuit breaker labeled "conv" is for your converter. You probably don't have an inverter as that takes 12V power and outputs 120V. The reason the converter operates when you plug it in is that it is trying to charge the battery. I don't know if the WF8955 has a constant duty fan or not, some do. I would suggest to blow compressed air through it or even disassemble, clean, and lube the fan. If the fan is still noisy, it can be replaced with a quieter one. Some on here will tell you just to replace the converter since it is a WFCO product and some of them speak from experience.