Odd whistling or squealing noise at idle and engine lite on.

The 98 3.5 has a new odd thing going on, a strange whistling noise which is loud at idle and the idle is rough too so the engine lite came on. This noise is constant, appears to be from the front on the motor, the motor revs fine and sounds good other than a rough idle. Im not sure on this one, looked around didnt see anything apart or pulled apart, all hoses seam attached. You guys have any ideas???

Could be a vacuum leak.
Have you have the CEL codes read?

Figured it out last night, a manifold gasket. This is a common problem I guess and I dont know if it has been done before but looks as a possibility. I changed upper and lower gaskets and its running better than it has for the last few months, so maybe this has been an ongoing problem which just surfaced by the whistle noise. Carb cleaner helped me find the area, by spraying it lightly the idle changed when I got to the area of the leak. Thanks for your comment and suggestion.