My thermostat housing started to leak and took about a month for me to notice it. During that time, a significant amount of coolant was bathing my engine parts. I replaced the housing and fixed the leak. But I noticed that I had a squeal coming from some of the pulleys on the belt now. So I replaced the idler pulley and the belt, and the tensioner was completely frozen so that was replaced as well. This worked for about 30 days until the new mystery took hold. When I use my AC system (heat/cold doesn't matter) the alternator lets out an ear piercing squeal. In addition, at low speeds with the AC on, the fan blows really loudly until I get up to about 30 or 35mph. I don't know if this is simply in response to the extra heat from the friction on the serpentine belt or if it's a whole new problem.