Onlyhavechevy

I just put a brand new 200-4r and torque converter behind my dads 327 sbc in a 66 el camino. It makes a distinct clicking noise when its underload in reverse or drive. (I can put it in park or neutral and rev it to 6k no unwanted noise) The noise is engine speed reliant, and is not engine knock. The noise is coming from the torque converter/flex plate area. All bolts are tight to the TC, flex plate is not cracked as far as i can tell. I cant imagine it would be the transmission pump if its a completely rebuilt transmission. I just cant find this damn noise. Im hoping that one of you guys can help me with this. thank you in advance!

forgot to mention that the tv cable is also set up correctly. doesnt seem to make the noise in 1st 2nd. only in 3rd drive and reverse. maybe sticking between gears....?