Serpentine belt squeals at startup, when in drive or reverse and when A/C turned on

In the past, I have seen pulleys that caused a noise simply because they had road dirt, oil, and other things on them that you really couldn't see. Just for the heck of it, try cleaning all the pulleys with something like brake clean. It won't hurt to try. Focus on the crank pulley. Keep in mind, if there is something there you can't see, it will already be on the belt, so take a rag and wipe it down really well.

Joe