Thank you so much for these replies...
I probably should've said in the original post - the main (and most infuriating) issue is the low hum from an air filtration system in the house (exactly the sort of thing you described DVDdoug)
Clepsydrae I've not had great success with ReaFir either so I may have to bite the bullet and buy something else. Sound Recovery by Bitsonic's had some good reviews and I've also seen this -
https://klevgrand.se/products/brusfri/
Thankfully neither of those options seem to break the bank but maybe you get what you pay for?
BenK-msx before I do ANYTHING however, I'm gonna follow your method for ReaFir!!
The other part of my question I maybe should've put in a separate thread...
When it comes to noise gating/HPF/EQ/Compression/De-Essing etc I guess I was talking about AFTER I've successfully gotten rid of the background hum. I'm confused about the order in which these things should be applied (assuming they're all needed/required) once the hum is hopefully a distant memory...
Is there a kind of 'standard' chain for voiceover from beginning to end before rendering?
Oh and I've realised when I talked about make up gain it was AUTOmake up I've seen differing opinions about, not make up gain generally!!
My bad!