The truck idles fine and runs good but it makes a whistling sound while accelerating or under any load situations. As soon as you ease off pedal it stops. In park, I can accelerate only to 3000 rpm then it begins to miss and the sound is very loud. I cannot pinpoint it but it it located on the driver's side under the intake. Checked vacuum lines, replaced injector seals, TPS sensor, and throttle body gasket. Noticed that an exhaust manifold bolt is severed. What have I missed?