Help with rough idle

Hello! Im new here and i just have a few questions.

I have a 1998 Explorer 4.0. It has 190k miles on it, and practically no issues except one thing. Im not sure if all of these symptoms are related, but i assume they are.

I went on a road trip this summer and it started to make a high pitched noise around where the alternator is while idling. It only did it a few times though, and only after long periods of time idling, which is rare. I thought it might be a barring, but its completely stopped making the noise as of now.
In late August the check engine light came on. P0171 and P0174. It idles rough as well now. I read online about the PCV and just tried to find it, but had no luck.

If someone could help me out finding it and maybe giving me some other ideas as to what may be the issue it would be greatly appreciated. Thanks!!

P0171 and P0174 are lean codes for bank 1(71) and 2 (74). I would suspect a intake vacuum leak. Maybe intake gaskets leaking. They can cause a high pitch or whistling sound . A howling noise could be the IAC valve sticking. I've also heard the PCV valve hose can cause a high pitch noise if split.