My mower never had any baffle, I have opened it several times right from the new and now the mower is about 17 years old. When I remove the muffler, I just see the piston through the exhaust port.
The baffle, if there is one, will be inside the muffler - it will not be in the exhaust port. Incidentally if a muffler rattles, it may have a loose baffle. (The other likely causes are a foreign object inside the muffler, or a broken attaching bracket.)
