Pontiac Repair: engine noise, spark plug wires, compressor clutch

Question
My 02 Grand am is making a very loud screeching from the engine and also codes are reading random misfire, o2 sensor and egr flow.  Im not sure if they could all be related since it all started at the same time.  But my mechanic couldnt figure out where screeching was coming from, if u could help.

Answer
Hi Ryan:
with out hearing it It's hard to tell you. I'll just guess, How about the a/c compressor clutch? does the a/c still work on this car does the noise go away if the a/c is turned on and off? if so that's your noise. As for the randon misfire either a bad set of spark plug wires of dirty fuel injectors. The EGR flow can be a few things from a plugged EGR passage in the intake manifold to a sticking egr valve it depends on what the actual ERG code is that can set a few different codes all related to the vlave but different issues with the vlave.. good luck :-}