With the vehicle safely lifted, have a partner start the vehicle. Plug the tailpipe with a large rag pressed over the end of the pipe. Note the exhaust leaks under the vehicle. It should be a simple job. Determine if the cause is a gasket, rusted pipe, hole, etc. That will dictate how you fix the problem. Don't forget to look under the hood as the problem could be at the exhaust manifold as well.