Had truck at work in northern alberta -35'c on high idle. truck all of a sudden started to sound like a helicopter. Went over to it and shut it off immediately popped the hood to see if anything obvious, nothing. fired it up again and a really loud continous popping sound. My airfilter was pulsating with the popping sound.r mechanic came over and thought maybe a bent pushrod or rocker arm and suggested do not drive it or run it at all. Anybody else had this problem?? if it is a pushrod/rockerarm can i just replace that one?