1984 BMW 323 Really Loud

It is extremely difficult for me to hear what you hear from cyberspace, however if the exhaust is an after market system, my first reaction would be to reinstall the stock exhaust system due to the fact that the after market exhaust systems I am familiar with do nothing for street performance and wind up just annoying people and relieving you of your money. Now that I have that off my chest, there may be an issue with a broken header pipe or a failed exhaust manifold that you might need to seek out local professional assistance to overcome. You may have a leaking manifold gasket, flange gasket or a cracked manifold. Get a length of hose and use it as a stethoscope to listen around the exhaust, if it is leaking this method will locate it.