Hello threedimen,
Your audiologist gave you part of the answer about the cause of the white noise/floor noise.
It’s maybe because of the dynamic compressor that you have floor noise. There is less nuances than in natural sound. An example would be the differences of nuances between electronic music VS classical music. The electronic music sounds like a wall of sound.
The classical music sounds more like the nuances we can hear in nature between a leaf and a truck.
Same for TV commercials VS movie.
A good way to avoid floor noise/white noise is to adjust the hearing aids more like classical music than electronic music 
Hope it helps a little bit to understand
ps: I don’t know your audiogram neither how HA are adjusted so I’m just giving how it works and is a common issue.