what Bernie stated, and after having listened to your video, my gut says it could be a pulley under too much strain; like a belt is too tight or an idler pulley is tightened too much or one of your pulleys could be conkin out on ya, including any from the timing section. But yeh, your pan has seen better days and if your pickup doesn't have enough clearance away from the pan, who knows what kind of wrong sucking noises it could be making?