I drive an '03 Ford Mustang. About two years back I was told I had an exhaust leak after I noticed my car had gotten louder. I was in high school at the time and didn’t have the money to fix what I thought was not a severe problem. Now I’m in college (still broke), but yesterday after I started my car I noticed the rumble had gotten quite deeper. I’m assuming I’ve just worsened my exhaust leak or damaged another part of the exhaust system by failing to get the original leak repaired.
On initial startup is when the noise is the loudest. If I let it run for a moment it dies down and sounds normal while idling. It only makes the noise as I accelerate and softens a bit after driving for 10+ minutes.