So I filled up today, I was going to use 87 just to make sure it kept making the same sound for when I bring it to the dealer tomorrow. However, the station was out of 87 and I filled up with 89. Still makes the same metallic pinging / clicking sound. Only does it on the highway on any type of grade. Never happens in the city except for one steep hill.

When driving, the sound seems to come from the passenger side foot well. I'm going to the dealer tomorrow, so I'll see what they say.

 

Some say they get a noise from the air cleaner box seal bad. But you probably have an exhaust leak.

 

Took a Ford tech for a ride, he said it's definitely spark knock. It's not an exhaust leak.

I'm dropping it off Wednesday and they're giving me a loaner car while they figure it out.

 

The issue was plastic retainer(s) that have something to do with the manifold. I forgot exactly what the dealer told me. Apparently they broke and there's a service bulletin about the 3.9 and the 4.2 having this issue.

 

To be exact, it was the imrc clips. There's a tsb for this issue.