It sounds like your 12 v Power converter may have a problem. I don't have a columbus but the 12 volt supply is likely a switch mode type regulator which uses a power oscilator to generate 12 volts with out the use of a large transformer. I've seen these "partially" fail in other (non-RV) applications where you would hear a sqeal that would vary with change of load.
Cathy & Jeff
2013 Sabre 32RCTS / 2012 Ram2500 Hemi
Nights Camped: 2015-140; 2016-137 YTD; 160 Planned