If there are apertures such that a mouse could access the belt it may be responsible for or have contributed to your problem. Several years ago there were acorns and mouse droppings in the V of my engine. Mice also significantly chewed the soundproofing foam on the underside of the top engine cover. Fortunately they hadn't chewed any cables or hoses. I set traps at various points around the engine when I wasn't driving the car and eventually I caught them all. Needless to say when I am doing under bonnet checks I also look in the V with a torch.
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