i have a 99 f-250 5.4. i have been hearing a knock at start-up.the longer it runs the quieter it gets.once the engine is warm you cant hear anything but an exaust leak going down the road.after i put my new flowmaster cat-back on the other weekend i was lookin and saw the top rear exhaust manifold stud on the passenger side was broke off with about 1/8 off an inch sticking out above the manifold yet.would that one stud being gone create that much noise when its cold?
also what are the odds of getting that one out without messing with the other seven?
thanks for the help

 

well iwelded a nut on the stud and it came right out.put a new one in and no more leak. i still have a knock at start up for a while but i guess thats piston slap?i have good oil pressure. but the flowmaster does sound good.