I was listening to some SRV today on Pandora, and The Sky is Crying Live came on. Phenominal playing by the way. Anyways, he does this thing where he bends a note up and then let's it ring and it goes from the note to like a feedback noise. How does he do that? Maybe it's a harmonic, I don't know...I've heard other blues players do it too.

VOX AC15 / AC4
Fender MIM Sunburst Strat
epiphone les paul custom in white
Yamaha FG730s
The Tweak-O fuzz pedal
thats happens to me a lot on accident, just feedback for me i guess xD
Jackson DK2M Dinky Pro W/ EMG 81/85 18v Black
ESP LTD EC-1000 W/ EMG 81/60 See Thru Blue
Schecter C-1 HellRaiser W/ EMG 81TW/89 Black Cherry
Peavey 6505 W/ 2x12 V30
Volume + the correct position.
Fender Classic Player 60s Strat
Washburn HB35
PRS Santana SE
Yamaha Pacifica 112MX
Vox AD30VT
Fender Champion 600
Dunlop wah
Danelectro Cool Cat fuzz
Turning to face the amp will get it to feedback easier. And there are certain spots in front of the amp it will do it better. Find the sweet spots and mark em with tape.