Exhaust System

Have your assistant place a rag over the exhaust while the engine is running. (Note they are not trying to block the exhaust just impede it)

Check system for leaks.
This will be a lot easier with the car jacked up but if you cannot jack the car up, a leak should still be more obvious when the pipe is partially blocked with a rag.

Joints are the normal places for leaks to occur and can sometimes be fixed by simply tightening up the bolts that hold the joints together.