Originally Posted by huntke
It only happens when plugged into land power
Check all ground and neutral connections. Then go check the same in your main power supply. Not familiar with electric stuff have someone that is. A loose ground or neutral in your main power box will cause this problem, same with your RV. Had a similiar thing with the appliances in my house once, I tightened all the connections and all was well.
If you have a "Main disconnect Switch" kill everything and then go to tightening, you'll be amazed at how many scrrews are not tight. That goes for the screw to the breakers too.
Good luck and let us know what you found......
Paul B - I am not an electrician but that is what I found with mine