I'm only on the third episode of season 3, but I feel like I'm noticing something that can't be just a coincidence. In multiple scenes now where we've seen this other speedster "The Rival", particularly when he's got the cowl fully on and we hear him speak, it sure sounds like they're mixing that guy's voice but ALSO with the guy who's the original Eobard Thawne/Reverse-Flash, this actor
http://www.imdb.com/name/nm0504762/reference
hell even in one of the Rival scenes (but he's not wearing the cowl) it looks like they're even fully overdubbing Letscher's voice to the other guy's face. One of the very few things I'm good at in this world is I'd like to think I've got a good ear for voices/accents, and I really don't think I'm looking up a blind alley on this.