I just noticed this today on the side of my garage. My Disco2 was backed up against it the night before while I changed out a rotor.
The truck runs fine I guess, and the only check engine lights codes are for the MAF and O2 sensor in bank 2.
I've been around trucks my whole life and worked in several restoration and performance shops, and I've never seen anything like this..

 

humid?
a couple of my trucks will do that when creating a lot of condensation. not so much on dry days.
I chalk it up to years of build up washing out with extra moisture in the air.


liquid carbon build up

 

That can cause black suit to come out your exhaust.

 

How about a charcoal pinstripe suit? Sorry, I couldn't help myself. I'll bet you meant soot, a carbon-like byproduct of incomplete combustion.

 

I was trying my as* off to figure out how to spell soot!! Thanks. I couldnt remember

 

Pretty normal during winter and in a garage as when the exhaust is hot it cools and produces lots of condensation internally and this spits out mixed up with soot from inside the exhaust.

(Did you know most carbon steel exhausts fail quicker from corrosion internally than externally ........... they say - I read about that somehwere, mainly condensation creating sulphuric acid from the soot )

 

Talking about soot....Fire up a Mack E9 V8 after it has sat for a week...it snows dry soot down from the sky.