I had a squealing start coming from the engine bay. I was out one day running some errands when I started hearing it at a stop light, so turned off on a side road and popped the hood to listen. It sounded like the alternator or idler pulleys, so I headed home. Once home, I thought I had pinned it down to the alternator. No surprise really, it is the OE, 20 year old unit. I ordered a good looking replacement on Amazon and thought all was just "Peachy". But, a few days later when she was all warmed up, engine bay hot, it started again... Whaaaat? At home I pulled the belt and started the truck, SQUEAL... well damn. I grabbed my long funnel I use for adding ATF, pulled the air filter assy and started listening through the funnel. It was coming from the area of the new vacuum tree at the back of the engine I had installed 2 years ago when I went to the 4 bbl manifold. It turned out to be a cracked vacuum cap Whistling when the engine got to temperature! Lesson learned, don't jump to a solution before really finding the issue.