How to play this kind of "growly" sound in the guitar?

Question

This is a snippet from "Ride across the river", from Dire Straits. Notice the distorted guitar sound at the beginning; is that sound a result of two close notes (e.g. a semi-tone or tone apart) played together, just a distortion pedal or both?

Snippet (starting at 2min40s of the full soundtrack)

Original song (roughly at the same point)

P.S. I'm not quite asking for the exact notes, since I'll not try to play that particular song. I'm just interested in how to obtain this "growly" effect.

Edit:

Just for information: I tried it at home with my keyboard and managed to find the notes. They're [F# A], [E G] in that order.

which is actually part of a VII - VI cadence (chords D - C) on the Em tonality.

I also noticed the "growl" effect of playing two notes with the overdrive distortion and the absence of that when playing just one note.

Answer 1

Interesting effect indeed!

Obvious thing first: don't use a pick when playing Knopfler parts! His tone is very much dominated by the particular way he plucks the strings with his fingers, often snapping them down on the fret board. Here, like often in his soloing, he's playing a double stop; he usually does this with the thumb and index finger, almost pinching together and dragging up the neighbouring strings and letting go of them. (Watch some videos of his solos; the right hand position looks really strange but works very well for this kind of stuff.)
This particular note has the characteristic attack largely shadowed because the tone is faded in à la steel guitar; note sure if he does this with the volume pot like Jeff Beck or with a volume pedal.

Now as for what he's actually playing at that particular spot... what I hear there is

X: 1
M: 4/4
K: Em
L: 1/4
V:C name="Guitar" clef=treble-8
z3 ([^d a] | [e g]

Which is essentially a ⅶ⁰ - ⅰ resolution, i.e. pretty classical dominant-tonic (except the bass and synth actually go to C instead of em, but that fits just as well to the E and G). The tricky bit is that the slurs are actually glissandi, i.e. bends – in counter-movement! Quite tricky, uncommon and certainly very effective. This can be done by playing the D♯ on the D string 13th fret with the ring finger and the A on the G-string 12th fret pre-bent (pulled, not pushed) one whole step with the middle finger, then releasing the G-string bend and simultaneously bending up the D♯ to E. It's just one movement.

Finally, again rather obvious, you need some overdrive to actually make it “growl”. Not a hard distortion, rather something tubescreamer-ish. Distortion on such a double stop creates intermodulation frequencies, i.e. basically tones that aren't really played on the guitar. Thus, as David Bowling comments, it's also possible that he actually just plays the simpler

X: 1
M: 4/4
K: Em
L: 1/4
V:C name="Guitar" clef=treble-8
z3 ([a c'] | [g c']

(which, at least when bent up rather than down, is quite a staple of bluesy solo playing), and the lower “counterpoint” voice is just imagined by my ears, being used to classical voice-leading.

Answer 2

From trying to work it out myself I found that playing Eb on the G string and Ab on the B string while bending up about a quarter step on both gives me the right notes. The tone is a combination of the distortion/overdrive and heavy reverb that permeates the whole song. Then bend the note back down and end on a Eb/G major third. The next line continues on the C above.

I also found that for the particular tone on that note you need to pick very lightly to reduce pick attack, preferably with the side of the pick or scraping the string lightly with your fingers to bring out some of the harmonics.