Loud Squeaking Noise

As an automotive technician, I don't like to guess, I prefer to diagnose. Guessing will almost always result in replacing un-needed parts. You can try spraying the belt with a quick shot of WD40 or silicone spray, if the noise goes away, you have a bad belt or the alignment of the pulleys is off. The key is to locate the source of the noise, you have a lot of rotating parts in the belt area, waterpump, alternator, p/s pump, idler bearings etc. and all these can make noise. I use a stethoscope and carefully listed to each part and try to locate the noisy part, this can be done with a large screwdriver too, but be very very careful!