Kind of sounds like you perceived him yelling at you when that isn't what was really happening. Perhaps a more forceful tone seemed to you like yelling? Maybe you just didn't like his message and felt scolded so you interpretted that as yelling? Sounds like when you said he was yelling, he disagreed but lowered his voice to barely audible (which would indicate that in fact he wasn't yelling in the first place or he would have just gone down to a "normal" tone of voice instead of barely audible).