What is this guitar technique called?

I see it in modern metal, but even Metallica has used it in the past

You basically alternate between palm muted (usually) open notes on the low E, and clean notes on the A (generally on frets 5, 7, 8, 10, 12 depending if you're in dropped tuning or not

Am I rambling or am I making sense? Is there a name for this type of riff?

here's an example, hopefully this comes out right (on iPhone not desktop)

A---7---8
E-0---0---0---0---
---

hopefully you get the gist:/

I You described it well. I know what you mean… And I found out what it's called.
the palm muted note is called a "pedal note"
http://fastguitartechniques.com/Playing-Styles/Heavy-Metal.aspx

I've done it myself many times, I just never called it anything.