Need advice on removing unknown substance from wheel well.

I washed my truck for the first time in over a year (shame on me) with the plan of fully detailing it with a clay bar and a fresh coat of wax to protect the paint and get it looking really good again. But my plan was ruined when I discovered this stuff all over the wheel wells. There's also a little bit down the side of the truck but not like this.

It looks like some sort of paint or something. I have no idea when it happened so I don't know what it is. I've tried bug and tar remover, polish, and compound and none of these methods have worked.

I'm looking for some ideas of chemicals that might dissolve it without damaging the paint or other methods that might work. I've never came across anything like this before while cleaning a vehicle.

 

I don’t think that stuff comes off without the paint also coming off. But I’d try waxing it. Might have to get that spot repainted though.

 

I can chip it off with my fingernail so I know it will come off. I'm just looking for a method that doesn't require a full day chipping it off little by little. It's all over all four wheel wells on the liners and mud flaps too.

 

In that case try a pressure washer.
If no luck with that wax it

 

Soak it with WD40 and see if it will soften up and wipe off.

 

Heat it up with a hair drier or heat gun and when its warm and soft spray break cleaner on a rag and it should wipe right off.