I wouldnt think they are too close as they should be about 6-8 feet apart from each other. But it does sound as if you are getting some interfernece. May check the frequency settings on both units and make adjustments as needed, Ive only run Lowrance so I cant help ya much on the H-Birds but there are a few on here who will be by shortly. I always like to have both options, one on the troller and one built in for the FWD unit, that way if i lose one transducer i still have the other to plug in and not ruin a days fishing.