Here's another challenge for you guys. I've been around race motors most of my life, but have never seen this before. I have a 496 c.i. gen 6 block, 13.5 : 1 J/E pistons, Eagle rods/ crank, Dart Pro 1 heads, aggressive cam (770 lift, 300 dur. approx.). This has just been assembled by a local engine builder, with some notoriety for building race motors. The motor starts, idles, and seems to be running fine, except for one problem. I hear a disturbing internal noise...hard to describe...kind of like a vibration, or slight binding, which fades in and out with the engine idling. I thought it was trans. or convertor noise, but I have nothing behind the motor, except the flex plate, and the noise is still there. The water pump is electric (CSR), and the noise seems to be louder on the driver's side of the engine. Any ideas? The rotating assembly was used in another block previously, with no problems, and it is almost new. Is there any possibility that this thing is slightly out of balance? Before you ask....it has the correct balancer and flex plate for an internally balanced motor. No balancing weights on either. Keep in mind....this is a newly built motor, which all the components except the block and the cam were used previosly with no issues similar to this. Thanks for your input.