Noise in my new 29 a engin

[pinball73]

ok guys I am new at this, but hear we go! I have done a complete rebuild of my 1929 ford model a engine! it runs great sounds real good until I get it warmed up & on the highway in third gear at what I am going to call a cruse, 35 mph or so. not giving it any gas & not letting off of it either! I get a noise I don't like & don't think is normal! at this point I can retard the spark lever & it almost goes away! can't think it is spark knock ! it sounds too much like something mechanical! tried removing the plug wires one at a time & it makes no difference in the sound of the engine, so don't think it is rod,main, or piston! it has been bored 100 over new pistons, rings & valves have been re done. Babbitt is good & crank has been replaced. oil pressure is good, I would like more, but that is what they say it should have, thought pistons might be touching the head, so I scoped the cylinders & find no evidence of this happening! this thing has me barking at the moon! has any body got any ideas? I need help