One cause may be lack of lubrication in the vocal folds and larynx.
I am not a vocal coach or instructor, but what I have experienced myself is that lubrication is not the same as hydration, so simply drinking a lot of water may not deal with the situation, and may in some case worsen it. Lubrication requires a proper balance of moisture and minerals. I am not a fan of supplements, so, I personally like to pay attention to everyday diet and watch for what improves or worsen my sound.
Diet is very personal. How much water you need will depend on what you eat, your alcohol intake, whether you smoke, etc. Then you have to make sure that the mineral and sugar intake (especially salt) is balanced with the amount of water, because minerals and sugars are what hold the water in place in the cells. Excessive water can cause the cells to dilute and leak, losing the benefit of the hydration. So, be careful with advice to drink gallons of water every day. A lot of your water intake could come from fruit and veg already, and how much is needed varies from person to person. If so, you wouldn't want to follow the same advice given to someone who drinks 10 pints of beer a day, and has no fruit or veg. (Personally, I think that current popular advice assumes a pretty bad diet, and is unsuitable for people with a reasonable diet.)
The fry sound may not be acceptable in classical singing, but I do come across it from time to time with some accomplished contemporary singers, although it is not constant (more occasional). However, if it is caused by lack of lubrication, I would imagine that it could cause damage in the very long term, if not attended to. I very much doubt if you have any vocal damage right now, though.