Haha. (1) that’s not the fuel tank, (2) looks like road debris, most likely from tar etc. especially after 17K miles. Can see many more “tar hairs” under there. (3) it’s NOT a big deal. LOL

 

Completely agree!

 

That’s the exhaust. Don’t see any issues, just a bit dirty.

 

That’s your exhaust back box! Clean it off and if it goes black again you’ve got a small leak in your back box, it doesn’t look like it’s hit anything and got damaged so will be covered under warranty.

If that damp patch on the floor underneath the black mark wasn't there before then it’s definitely a small leak in the back box, it will be condensation drip marks which would normally leave the exhaust pipes as a gas

 

Clearly you’re blind and/or know nothing about cars, hence shouldn’t be offering up advice (confusing the OP). It is so obviously tar. It’s all over the bumper as well. Exhaust leak looks NOTHING like that.

This is how misinformation spreads, intentionally or otherwise. /rant
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