I don't think this is normal, I had read somewhere that some people had humming issues with that unit the E series, and it said something along the lines to contact customer support at Rigid. If you google the following
"rigid industries 40 e series led light bar humming issues "
a detail about the Rigid face book pages comes up with the following.
"If you are having humming issues with a light bar, please contact our sales team"
I would call them just to make sure. It may be normal that it will hum due to the heat its generating hence the heat sinks but maybe not. best confirm with them.