Had to strike the first line, happens to me too!
I haven't researched it, but I'm guessing the hearing aids just inject a bit of noise to mask the internal noise.
Though I do recall some research (probably in an old thread), that some very specific types of noise actually helped. It might have been like using noise, but filtering out the noise we hear in our head, so it isn't noise on top of noise, but then a constant level across the frequency band. And that would maybe calm down our brain's response? Something like that?
Tech Note: While most people will refer to it as "white noise", in most cases "pink noise" is used for audio masking. White noise has equal energy at all frequencies, pink noise has equal energy across each octave band. That means pink noise has the same amount of energy from 100 Hz to 200 Hz ( a pretty narrow range of bass-to mid-bass tones), as it does from 4,000 Hz to 8,000 Hz (a wide band where a lot of consonant sounds are. So to our ears, there is more emphasis on the lower frequencies. Some noise sources allow you to choose.
If you take white noise (the noise between stations on an un-muted FM radio), and turn the treble tone control on the pre-amp or receiver all the way CCW, that's fairly close to pink noise. Not as 'bright' sounding.
-ERD50