So I recently did some highway driving, I noticed when I got home that what I'm thinking the exhaust is making like a metal liquid noise/ pinging on a way, sounds like it's coming from the exhaust..wondering if anyone has ever had this noise.

Seems like it comes mainly if I drive the car long and or hard.
Thought came it is either a cat converter but mainly thinking it in a bad resenator, bad I had a bad resenator before and it was more of a rattle noise from the inside..

Any help would be great, seeing if anyone had any problem similar, exhaust is a magnaflow/flow master.

 

That's your pipes cooling down, you must be driving a bit hard for it to do that. I've given my car a fair push at times and have never had that happen. I do not know what part is involved, or technical wording, but from my experience, that is your pipes cooling off/down.

 

^ this

 

Can't say if my TL does that exactly but over the years I've had plenty of cars that click away in the garage as they cool. Metal expends when hot so as it cools anyplace there are pipe connections is prone to some stresses that relieve in minuscule "steps". The parts clamped together don't cool identically, so they don't shrink identically. There is friction and when enough stress builds it's released and you hear it as a click/pop. It's not like you can see anything move. You just hear it since the exhaust system is so good at amplifying sounds. I've hear manifolds let out some good pops too.