An exhaust restiction, like a clogged catalytic convertor
Probably a rotted exhaust pipe has broken off. Take the car to a muffler shop for repair.
An exhaust leak could do that.
a dining sound could be lose nuts on the exhaust
exhaust leak, bad hangers on exhaust, or the catalic convertor, its one of the three
A hole in the muffler would cause a knocking sound in your muffler. A loose exhaust pipe can also cause a knocking noise.
Loudness: Sound power is the cause, but sound pressure makes the effect. Scroll down to related links and look at "Sound pressure and sound power - Effect and cause".
The muffler is failing, the "floss" is how the exhaust sound is muffled.
Well, any change to flow of the exhaust gases will change their sound. That said, how much of a change in sound depends on how much you change the flow. Tips, normally go over an exhaust pipe and perhaps extend it a very small amount. It is unlikely this would cause much change...up or down.
Fog?
No, but it will make a sucking type sound.
Take it back immediately to who ever did the exhaust work.
muffler or exhaust could be damaged....if it has aftermarket exhaust it will sound different since it is not a V8.