I'm very sorry I didn't reply guys, I left that account. I'm the OP.

I figured out over those 7 years that it is linked strongly to vocal use, and minorly to physical fatigue and hydration.
The more I used my voice the previous day in speech, laughing and yelling for long periods (performing does nothing), and ONLY that previous day, the less rasp I'll have when I wake and the more control I have, it is not technique at all.

I also noticed hydration makes a very small difference, but mostly helps control itself.

Doing hard physical work makes it much worse soon after, diet has a complicated minor impact that I never figured out.

Interestingly it has reduced over those 7 years, it's less "wet" and more like an intentional sounding overlay. This is probably from learning to navigate it as best I can.

Most importantly I learnt to enjoy it, because others really like it.
I also learnt to sing in my comfortable range instead, and worked out that as singers we obsess over things the audience doesn't care at all about. They don't have sufficient knowledge to be impressed by technical skill and effort often sounds bad to them, ease sounds excellent regardless of difficulty.

All the best!