This one time at sound camp...
I had our "certified" sound guy complain once about noise in one of the studios.
He had a mic channel open, with mic levels pushed to max and the headphone monitor turned up all the way.
And yes there was some hiss and yes, room noise.
So I took the mic off and put on a tone generator and had the sound guy adjust for 0VU on the console and a comfortable listening level in his headphones. Then I removed the tone and put the mic back in. I asked him how it sounded. He said fine. Then he said, but here is the problem. He then cranked everything to max again.