Sqeaking noise under the hood

I have a 2002 Ford Taurus 3.0 12 V regular gasoline. Recently there has been a pronounced "sqeaking noice" almost like birds chirping. It's not coming from the belt. In the past it has done it sporatically but passed it off has the belt...because it went away. Yesterday I really noticed it....but ran just fine. Now today the engine light came on and it runs like crap....hesitates. The codes read bank 2 lean or rich...cylinder 5 misfire and bank 2 sensor 1 switch. Camshaft sensor and/or synchronizer was a thought...now this happened. I'm confused. I don't want to get parts that I know will not fix the problem...or spend too much money on a shop ifd I don't need to....thanks