97 f250 7.3 zf5 158k miles. just drove up to wyoming from colorado and it ran awesome all the way here, truck started making a low hissing noise at idle and goes away when i goose it, sound doesnt last for more than 10-20 seconds, i just put an AFE intake on, so no boost/intake leaks, changed my oil and that helped slightly, but it came back, also crank times are longer, starts rough, idles fine. also noticed slight power loss during the noise. about to go on a long drive so please help. sounds seems to be coming from drivers side of engine.