Way back when we first bought our '72 in 1980, one stock muffler 'jingled' at idle. Turned out that ANSA had added a "final baffle" inside each muffler by tack-welding a steel washer inside the muffler onto the perforated outlet pipes. And in 8 yrs of driving, the tack-welds broke in one side, freeing the washer to fall into the muffler case to rattle around.
Cutting a little hole in the case allowed enough access to dump the thing out. Then I took a piece of steel pipe and stuck it in the still quiet muffler outlets. A sharp whack on the pipe end easily broke those washers off too and I removed all of them the same way. The noise increase from the four broken 'final baffles' was un-noticeable.
IMHO, anyone not rather well to-do that owns any Italian car and does NOT own a large selection of tools, welding equipment and a lathe, is fighting an uphill battle if he/she expects to drive it regularly! Sure- there are shops that do this stuff every day.... at $80-$125/hr. And they have waiting lists.