This intermittent squealing sound is terrible. Firstr they said it was the belt. I changed it. Then they said the tensioner. I changed it. then the alternator. I changed it. Still get it, mostly when engine is cold. Seems to be coming from rear of engine...really difficult to pinpoint it for sure. Can't see anything back there. I figure it's either camshaft bearing, the transmission converter or the rear main bearing although I've never heard this noise before in all my 50 plus years of fooling around with cars.

Update from Feb 24, 2011: FINALLY found the noise.......I forget the actual name of the part...something like AFS...automatic fuel sensor...or something like that....anyway...it sits on top of the oil pump shaft back where the distributor use to be. It actually controls when the injectors get fuel. Seems there is a bushing in this shaft that when worn squeals intermittently. Had to get a complete intake manifold gasket kit as it needs to be removed to get at this thing. When it was finally out, I turned the lower shaft and you could hear the squealing sound. Replaced it...all fixed! If you think you might have this problem, get a mechanics stethescope and check it out first before replacing everything that runs off the belt up front like I did!!!!