It makes no "knocking" at all at idle. You can rev it up as high as you like and there isn't the slightest sign of the noise. The truck used to knock (or I guess ping) under heavy acceleration soon after I had the motor rebuilt but I had a mechanic do a tune-up and it completely went away. Also, when I adjusted the timing the other day, it actually effected how much pinging it made. The motor makes more of a "rattle sound" as Dan said, than anything else, I guess this is a good sign?

1966 Chevrolet C-10 LWB
1965 Chevrolet C-20 LWB