Update: Well, I got brave enough this morning to at least say something, but I didn't want to appear rude or bossy, so I went up to the couple (both about 50ish) and asked, "When you receive communion, do you put the gum under your tongue?" The husband nodded, while the wife said, "Yeah, usually." "Oh, I just wondered." I said. As I was walking away to catch up with my family, I heard her call after me, "Why? Does that bother you?" I looked back briefly and just said, "Well, it's inappropriate." Well, she let out this high pitched screechy laugh that everyone could hear and then proceeded to say things to me that I tried to avoid and we got in the car and left.
Boy, do I regret that!! Now at Mass they will point me out and I will have to deal with the embarrassment of having a confrontation with them. Not good. My husband said I shouldn't have said anything to them, that it was none of my business.