If your vehicle begins making a louder noise than usual, you should suspect the muffler needs replacing. This is a job best done at a shop because it is difficult to work under a car without a lift. You can get a warning or even a ticket if your muffler sounds too loud.
If you are worried about an auto body shop puffing up the amount of work that needs to be done, go and get free diagnostics from somewhere else. Since there is no guarantee you will get work done by them, they have no reason to claim there is more needed than necessary.
Every time your car is repaired, regardless of how minor the problem was, make sure you keep a record. If you have problems later, these records can come in handy. These records will make identifying issues much easier to diagnose and will save you time …