I can see giving him a bit of time to settle in to a new place , since you just bought him, right? but, a day or two should suffice.
stop looking at external things as reasons for why you cannot expect him to pay attention to you. to get a hrose's attention, you must become IMPORTANT. right now, every thing that rattles a gate is more important to him. that would make me a bit angry, to be honest, and it would help me become big enough to make that horse look at me like, "hey!? what's this right here? I better pay attention, 'cause it's something important!"
Start rattling the gate louder than the other guy!