Watched the video,not sure about the noise could be pto rattle being that it goes away when engaged, I've had the bolt that holds the gen bracket behind the starter pulley come loose and back out to where it starts grinding and banging on the pulley especially if the pulley got some bends from being pried off. Has nothing to do with the noise but if you replaced the head gasket it's always a good idea to re torque the bolts after its been run a while or maybe you've already done !
