A few of you have stated that your blower fans squeal or screech. I'm guessing that that may be due to lack of regular use, or age of the blower. The blower on our boat (can't remember the brand, but I've seen it advertised not long ago for only $35.00) is at least 13 years old (length of time I've owned the boat) and I'm thinking is likely the original, as maintenance records from prior owners don't show it being replaced. And it doesn't squeal at all, only sounds like a strong rush of air out of the exhaust vent, but not unpleasant. In fact, once or twice when I have used it while motoring on a hot day, I forgot it was on, only remembering when I did my usual check of all the instruments and gauges while underway.
I don't know if there might be a way to spray silicone or some lubricant into the fan spindle to quieten a noisy fan, but might be worth a try.
Frank