Today I was driving my 66' when suddenly it began knocking severally for no apparent reason. Since the tank was nearly empty, I drove to the gas station and filled it all the way up with 93 octane gas without ethanol, no change in knocking. Even if you hardly give it any gas, it will begin with what I assume is, severe knocking. It has been around 3000 miles since the last oil change, the truck it not smoking and has plenty of power. The motor is a 350 V8 with 4 barrel carb and an RV cam with around 15,000 miles on it. Any ideas? Thanks

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