First we need to clarify the issue and terminology a bit. Your unit may have both a power Converter and an Inverter.
The power Converter changes 110-volt AC to 12-volts DC to charge the batteries and run many of the the RV systems. It has fans (mine has two) that will run when the unit is loaded charging the batteries from a low state and/or supplying a lot of coach needs like when we have lots of lights on, the furnace running, water pump on, etc. The power converter is generally part of the circuit breaker/fuse box and usually located inside the unit where any sound it makes is apparent to those nearby. Mine is in the main bedroom.
The Inverter (if your unit has one) changes 12-volts DC (battery power) to 110-volts AC to run a few select appliances when you are not hooked to shore power or running the generator (if equipped). In my unit my inverter will run my bedroom and front TVs and my microwave. That's it. My inverter is located in an outside compartment and also has fans that run whenever it is working, but I cannot hear them at all inside. However if the inverter is inside and being used in your particular unit it would not surprise me if the fan ran continuously whenever it was inverting power.
I have heard where some power converter fans run constantly even though there is little or no demand, they were defective and a replacement solved the problem. But you have to rule out that it is not under a heavy load when the fan is running to make that call. Very low or defective coach batteries can cause it to be under load constantly and cause the fan to run continuously. The fan is doing its proper job under those circumstances.
2014 Seneca 37TS
Toads: 2014 Ford Explorer Sport or 2013 Ford Focus ST