(Cringing) My 2 cents. Coolant evaporates from AIOs, some more than others. I have my clients replace them about every 24-36 months. If they don't want to spend the money, then I find a way to drain them and refill with good coolant. Done probably 6 or 7 that way. That noise is friction and it's going to take a toll and kill the impeller. Not gonna get better on it's own, only worse. Whether it's actually cooling okay or not is irrelevant, it will pass a threshold. Could even leak from the constant vibration.