Can someone push their AFM door open (to trick the ECM into thinking air is flowing) with the key on, engine off and tell me what sounds you hear around your fuel rail (under the intake plenum)?

I'm trying to troubleshoot my truck's random crappy running and I hear a distinct hissing when I do it (I just pulled the intake tube off the airbox and throttle body and pulled the door open from there.)

Not sure if that's a normal sound or if I might have a stuck injector...

Thanks!