I liked my 96 XJ 2wd so much that I bought a 96 XJ 4wd. But I have a question.

There is a strong smell of gas coming from the Jeep when you approach either the driver door, or passenger door. It smells even when the engine is off.

I looked under to see if there was any leaks, and I can't see any at all (before, during and after driving it).

The exhaust sounds like it needs a new muffler, and it certainly vibrates more than my other 96.

Any ideas on what this is, or how I can check it myself without having to pay a mechanic?

Typically, strong gas odors come from fuel leaks. If the fuel line has a pinhole in it from metal fatigue or rust, or a loose fitting/component the resulting slow leak can soak down adjacent areas. But gasoline evaporates so quickly, all the gas dries up before it can accumulate anywhere to start dripping.

The problem here is gasoline vapor is more volatile (flammable) than liquid gas. Imo this problem is serious and needs to be remedied before you drive the vehicle anymore. Usually a mechanic can easily find the source of the leak when the car is on their hoist.

BTW, sometimes a problem with the Evaporate Emission Control system can cause a gas smell, but this is not common when the smell is considered to be "strong".