'07 450 work truck 6.0 96K miles on it, runs great but I've noticed the last few days that when sitting at a stop light idling, that I heard a humming sound inside the cab. Found that the humming sound is coming from the lift pump on the left side frame rail. Would this be an indication that the pump is headed south? I need this truck on the road in a bad way. Is it too much trouble to change out the pump? Thanks!