I recently replaced the lower manifold gaskets on my 99 bonneville se, along with the uper intake. After finally finishing the project, i get this awful squeal from somewhere, i dunno where, but it only happens at idle. When my rpms get around 1500, the squeal goes away. I removed the belt and spun the pulleys, thinking it could be one of them, low and behold, my alternator squeaked a bit. I replace that today and the squeal is still there. Is there any way to properly align the alternator (it coud be out of alignment with the other pulleys) There is also no belt diagram on my car, and i think i could have possibly routed the belt wrong (there is no diagram in the haynes manual i have either) I'm not even sure that this godawful sound is coming from the pulleys (i'm just kind of hoping a lot) cuz it seems to be the more inexpensive route. Any suggestions are welcome along with help on the other things i asked about...Thanks all

Does the squeal go away if you open your oil cap?

for the belt diagram get you a chiltons or haynes or other manual of the sort. how much was your alternator?

Have you replaced your PCV valve lately? I had the exact same symptoms as you're having. I replace an idler pulley & a water pump before figuring out that the O-ring was not seated properly around the PCV valve. Like someone else mentioned....does the squeal go away when you remove the oil cap? Most likely, you're just getting an enormous amount of vacuum inside your crankcase.

i sheepishly admit that i didn't transfer the pcv valve. I didn't realize where it was located. When I installed my new upper intake, it came with a new MAP sensor mount. I coldn't get the old one off so i just threw the new mount on and went on my way. I was flippin through my haynes manual last night and discovered where the pcv was located... Woopsie. I went to my local dealer today and picked up a pcv kit ($12) and that seemed to take care of it. p.*. my alternator was around $180, however my alternator was noisy so i did need that anyways.

I figured it was the PCV

That'* where I was going with that. The oil cap test is a dead giveaway. Glad you got it fixed EASILY.