I look primarily for two things (both have already been mentioned above):
1. I want a nice limber (floppy) brisket. I want it to nearly fold in half IN the cryovac. If a brisket is real limber when it's raw, it'll be more limber when it's cooked (as long as I don't fark it up).
2. I look for a nice thick flat at the end opposite the point. Many briskets will really taper off and get real thin at that end. Those are the ones that typically overcook on that end. I want my slices nice and tall throughout the flat so I look for a nice thick, uniform thickness throughout the flat.
What I have NEVER done, however, is put it to my ear and listen to it.
But....heck.........with our brisket scores this year.....I'll try anything once.
I'm curious though, Full Draw BBQ, what should it say back if it's a good'n?