High gear noise ??

[bogdonj]

I recently installed a new rebuilt engine, balanced crank,flywheel etc, in my 31 sedan and noticed now that I have grinding type of noise when in high gear and really noticeable at low RPM. when I speed up it is a lot less noticeable and when I engage clutch it goes away?? this only happens in 3rd gear. I don't recall this happening before new engine was installed which is why I didn't have anything done to transmission while motor was out...any ideas??