Even though you said you aren't, you may be lactose intolerant. Most of the protein sources you are consuming are derived from milk.
Usually these shakes that have Aminogen, or Protease on slapped on the label, usually don't have very much of it.
I get gas all the time and it has Aminogen.
Try supplementing with a Separate Protease digestive enzyme with each shake.
I know Dymatize Elite has a good amount of , maybe give them a try.
BTW, does this happen when you consume whole food animal protein as well (fish, Beef, Chicken) or just shakes?