Exhaust leaking in front ?

[David C]

Hi, I'm hearing a high pitch squealing that ressemble that of a squeaky belt, but definitively comes from the engine itself. It's like some sort of constant whistling and I'm not too sure what to do about it, I suspect it's also causing my car to loose power or perhaps to raise my fuel consumption, as I'm not getting as good of a gas mileage as I used to in the same conditions. The sound kicks in mostly when there's a higher load on the alternator at idle, but also will stop when I let go of the throttle during deceleration and come right back when press the gas pedal. Could it be a leaky exhaust gasket near the exhaust manifold ? Alternator pulley bearing ? Wondering if I can tackle this or if it's a repair shop level job. 2007 3dr HB auto.

Thanks