yep, me too. i notice it whenever i eat any so products like soy milk or meat replacements. So drink rice milk instead (rice dream vanilla flavored is awesome!!) and i dont have any problems when i drink that.
Do you have the same effect with all the brands of soy milk you've tried? It could be an additive like carageenan (algae used to provide a thick texture) causing the gas.
I found soy milk made me gassy at first, but since I've been drinking it exclusively for a number of years the effect seems to have passed. So it might go away once your body gets used to it. You could also try having smaller amounts of soy milk more frequently and see if that makes it easier to digest.
Gawd, I was just mentioning this too my roomate/friend after we bought some soy cheese, soy milk, soy nog, and soy ice cream. \\<.< I've always been gassy, but I've been super gassy since I moved in with her. Boy do I have stories about it when I was at work. ^.^;;;
<.< I just realized tonight alone I had soy sour cream on beans, soy nog, and some soy milk. Yay below the aura of stench around meeeee.