[batmmannn]

Well if it is from the exhaust yes they can make noise but it is usually not a knock. Did you install the engine? Could be the manifold gaskets. Do you feel any air pushing where you hear the sound? Usually if it is so compressed that it could sound like a knock it would be a small leak in the gaskets or a hole in the header pipe. Check were the exhaust manifold meets the first pipe there is a gasket that goes in there. See if you have air escaping there. Have you looked all this over? Take a very large screwdriver put one end on the place you hear it from and the other against your ear and see if you can trace it as being in the manifold or in the block. If it doesn't sound like a woodblock then it's probably exhaust.